|Volvo 240 Mods
Just a few cool mods to keep you sane and properly entertained.
|UPDATED: October 30, 2020 CONTACT|
O M A I N S
|N A V I G A T E T H I S P A G E|
|240 VIN Decoding Page
|240 Power Mirror and Mirror Switch Page
240 Fuse Panel Page
||Fuel Pump Relay Mods and Fixes|
|DIY Front Toe Alignment||Improving 240 Gauge/Dash Lighting
||240 Dash Top Gauge Pod Project
|240 DIY Small Clock Repair
||240 Gauge Cluster Mods
||240 Smog Emission Compliance
|240 Gauge and Electrical Diagrams
||240 Rear (taillight) Bulbs||Fog or Driving Light Wiring|
|Cadillac 4-Note Horns (LOUD!)||Electric Cooling Fan Info||4-Speed Fan Controller|
|AutoCoolGuy PWM Fan Controller||Painting 240 Taillamps||Stepper Idle Valve Project|
|240 Interior Refresh||240 Door
||240 Exterior Paint Renew|
|Yoshifab Turbo Oil Drain Tube||Yoshifab Catch Can Install||Oil Cooler Information|
|Oil Cooler Thermostat||240 Door Top Black Vinyl Trim||Electric Power Assist Steering|
|240 Steering Rack Identification||Classic Car Insurance||Classic Auto Air AC Installation|
|Bigger-Better ALTERNATOR for your 240
Cracked 240 Dashes Better
||Rear Wheel Spacers|
|Wider Rear Wheel Clearance||Calculating Wheel Offset||Momo Steering Wheel Hub Fix|
|240 Headlight Switch Plug||240 V Belt Sizes||240 Headlight Switch Plug|
|Super Bright Dome Light||Gentex Mirror Upgrade||Guide for CRIMPING TERMINALS|
|240 Hydraulic Clutch Info||240 Driving Light Brackets||Lowering Your 240|
|240 Cup Holder Project||G80 Diff in your 240||Fixing Underhood Grounds|
|Benefits of Zinc Anti-Corrosive Paste||HARDWIRE Your 240 Taillights||Quick Taillight Repair (FOIL)
|Later Windshield in your 240||Headlight Relay Harness||The 240 Headlight Step Relay|
|Step Relay ELIMINATION||Speedo Recalibration||Bulb Failure Sensor PART 1|
|Bulb Failure Sensor PART 2||Bulb Failure Sensor PART 3||Faster Better WIPERS|
|Mods using RELAYS||Komfort Blinker Upgrade||M46 OD Harness|
|Auto Trans OD Harness||M46 / M47 Shifter Knob Fix||In-Tank Pump Upgrade|
|240 Tach Install||Plastic Fuel Line Repair|
|240 (52 mm) Small Tach Install||Bad 240 Door Lock Wires||Temp Compensation Board|
|I like 240s a lot and there's
nothing I like better than modifying them for
performance, handling, comfort, etc.
In this page I have outlined some cool mods I have done to my 240s and others that have been provided by other 240 enthusiasts.
Your comments are welcome: CONTACT
|240 VIN Decoding Page
CLICK HERE OR CLICK THE IMAGE
|240 Power Mirror and Mirror Switch Page
CLICK HERE or CLICK AN IMAGE BELOW
|DIY Front End Toe Alignments
Building a Trammel Bar
I built my own trammel bar nearly 20 years ago after learning about it online and I haven't had a reason to take a 240 to an alignment shop for toe adjustments since then.
A Trammel Bar can be very accurate and it's easy to build using scrap parts and its very easy and quick to use without needing a helper.
The main bar I used was an old u-channel aluminum extruded curtain rod part. It's very stiff, so it doesn't flex much at all. Total length is 60 inches. Plus I used a couple pieces of sheet metal and a metal ruler, all riveted together as shown below.
I generally find a line in the tire tread (or you can scribe or draw one with a marker while spinning the tire) and use that to measure. With the car on the ground, I measure the track width at those marks. One measurement on the tread facing forward and one measurement on the tread facing rearward. You can easily adjust for 1/8th inch toe-in or whatever spec that's recommended for your car.
1. Place the tool on the floor with the end pieces upright, pointing at the sky. For a measurement at the front of the tires, place the bar on the floor with the LEFT upright piece against the LEFT tire tread (align an edge on the upright with your drawn mark or a part of the tread.
2. The RIGHT upright with the ruler can be placed against the RIGHT tire and you can find a measurement or a scribe mark on the tread using the ruler.
3. Pull the tool out, turn it around, and do the same thing at the back side of the tread.
Compare the two measurements.
For 1/8th inch toe in, the measurement at the front of the tires will be 1/8th inch shorter that the measurement behind the tires.
Even if you still plan to visit an alignment shop, a tool like this will get you set up just right after replacing a rack or other front end parts and then you can verify your work at the alignment shop.
Here a good page to read about DIY Alignment with more Trammel Bar pics:
And here's a similar method of someone using a very expensive professionally built Trammel Bar:
This looks like the bar he is using: https://www.amazon.com/Longacre-52-79620-79620-Toe-In-Gauge/dp/B001NNFZ2Q
There are other methods, such as a string alignment. Long video here:
|240 Fuse Panel Diagrams and Inner Workings
I've created a page all about 240 fuse panels. Lots of details there.
CLICK A PHOTO ABOVE TO SEE THIS PAGE: Or CLICK HERE.
|240 Dash Top Gauge Pod Project
Project page for my dash top 3-gauge pod: https://www.240turbo.com/dashgaugepod.html
|240 Gauge Cluster Mods
A customer sent me some pics of his modified instrument cluster, so I thought I would share.
|Dealing with 240 Smog Emission Compliance
Since I lived in California for most of my life, I have plenty of experience working to make 240s emission compliant. This can be a huge source of frustration and it can be very expensive if you have to resort to paying someone every two years to work on the car for you.
Don't give up. The below discussion thread is a really good one. It offers a lot of good experience from people who've ultimately been successful and the thread itself is a great success story.
And a great article on this subject (also highlighted in this thread):
|Improving 240 Gauge and Dash Lighting
CLICK THE IMAGE
240 Instrument Cluster Diagrams and Gauge Electrical Fixes
Here's a growing collection of 240 gauge info that can come in handy if you're doing your own work on your 240 gauges or instrument cluster.
Click an image or go HERE: https://www.240turbo.com/240gaugewiring.html
240 Rear Light Bulbs
|240 Fog Light or
Driving Light Installation
Cadillac 4-Note Horns in a 240
I did this recently in my 240.
Options and Experiments in the Installation of a
Primary Electric Cooling Fan for your 240
When in good working order, the original belt-driven clutch fan in your 240 can handle most cooling needs. But if you have been thinking that your 240 needs an electric primary cooling fan, here is a page I put together on my experiences with a number of electric fan conversions over the years, from small 14 inch GM fans to big Ford or Lincoln fans. Plus a variety of wiring diagrams are included for building your own relay fan control systems if you like.
Cooling Fan Controller Project
(for my LINCOLN MARK VIII fan)
In 2016 I got tired of failing high-tech fan controllers that would burn up after a year or two when trying to control my big Lincoln Mark VIII fan. They always failed in the worst places. So I decided to design and build my own fan controller with FOUR speeds using what I know. RELIABLE RELAYS. Works great! You can build one too if you like.
Click here: https://www.240turbo.com/fanharness.html
|AutoCoolGuy PWM Fan
(for my LINCOLN MARK VIII fan)
New addition for My 242 Turbo in 2018.
Click here: https://www.240turbo.com/ElectricCoolingFans.html#autocoolguy
Painting 240 Taillamps
I get questions about the taillights on my car occasionally. These lights originally began as ALL CLEAR lights like in the below photo. At the time, finding half-clear lights was not possible. They can be found on eBay now. I didn't want all-clear lights, so I painted the bottom lenses myself using the below Testers transparent red paint, 1605 Gloss Custom Red. This paint is easy to use and goes on pretty well. It takes several light coats to get to the shade of red I got. Let it dry between coats and keep adding paint lightly until you have the red you like. It will slowly darken with each coat. These lights have been on my car for well over 10 years and still look new. Part of this reason is the car is always garaged.
If you need to tint in AMBER, I have not tried any transparent amber paints yet, but I have heard of good results from the below Tamiya TS-73 Clear Orange for Plastics.
I have also read that you can get good results from a transparent STAINED GLASS paint. Kyrylon makes such paint in aerosol in ORANGE and RED. I have not used these yet.
Stepper Idle Air Control Project
In 2018 I began working on a stand-alone manually adjustable idle control valve for my car using a GM stepper IAC motor.
Click the above images or below link to see it.
240 Interior Renewal Project
THIS NEEDED TO BE SHARED.
This discussion thread below began in May 2018 and it's a goldmine for inspiration on making your old 240 interior look brand new again. It's a great resource for information on paints and interior parts too, so I had to share it here for those of you who haven't seen it.
240 Door Card Build Project
THIS NEEDED TO BE SHARED.
This discussion thread was shared in December 2018. If you're patient and handy, it shows a great tutorial for you to remake 240 door cards to replace the old, warped or rotton ones in your 240.
240 Exterior Paint Renewal Project
This discussion thread below began in 2015 and outlines a 245 owner who went the distance in restoring his newly acquired 245 exterior paint to look exceptionally nice. His efforts paid off. It's a great inspiration to 240 lovers.
Turbo Oil Drain Hose for Volvo Turbo Red Blocks
Yoshifab Catch Can (breather box) Installation
|Volvo Red Block OIL COOLER
This information may come in handy when working on oil cooler systems on red blocks. The oil flow direction was important to me when I decided to install an in-line oil cooler thermostat between the engine and oil cooler. My factory 240 oil thermostat seemed to be no longer working and stuck in the wide open position. The new in-line thermostat required specific flow direction for "in" and "out" ports.
The factory oil cooler thermostat in my 240 Turbo oil filter plate seemed to have stopped working. My guess is it was stuck in the wide open position, since it was taking forever for the engine oil to come up to temperature. So I decided to add an IN-LINE oil cooler thermostat in the lines between the engine and the oil cooler.
Removing or Replacing 240 Door Top Black Vinyl TrimI gets lots of questions about doing this kind of work or where someone can buy these black vinyl trim pieces.
They have not been available for a lot of years from Volvo or any other source, but if you're persistent, good results are possible.
If you want new black vinyl for your 240, contact me. I can supply the new stripes you'll need.
CLICK HERE: https://www.prancingmoose.com/doorvinyl.html
Electric Power Assist Steering
If you like having power steering, but for some reason the traditional hydraulic setup isn't quite right for your modified Volvo (or if you want to convert an older manual steering Volvo to power assist) here are some possible answers.
A number of years ago, Josh Sadler of Yoshifab converted his Volvo 242 to electric/hydraulic steering. Josh's system was failrly simple. It used the original Volvo power steering rack. He mounted an electric/hydraulic steering pump and reservoir from a Toyota MR2 in his trunk and had hydraulic hoses made to route all the way to the stock steering rack. The result worked pretty well.
Here's a discussion thread on his installation: https://turbobricks.com/forums/showthread.php?t=135556
See his YouTube video below.
Here's another more detailed thread on a different MR2 pump installation in a Volvo: https://forums.tbforums.com/showthread.php?t=247548
And here's the next generation mod.
Steering Column EPAS.
It's an electric power assist (EPAS) unit from a Saturn Vue, Chevrolet Equinox or Pontiac Torrent. It's mounted in the steering column, so the level of tech is much higher.
This was an installation under the dash of a Volvo P1800 (pics below).
See the discussion thread here: https://forums.turbobricks.com/showthread.php?t=341174
Here's a supplier of just such kits that you may be interested in seeing: http://www.epowersteering.com/index.html
240 Specific: https://forums.tbforums.com/showthread.php?t=334886
Identifying a Power Steering Rack in your 240
Classic Car Insurance for your Classic VolvoThis is a bit of an unusual subject for a mods page, but I know it will be helpful to some Volvo owners out there.
Classic Auto Air all new Air Conditioning InstallationI finally grew tired enough of my mediocre Volvo AC in my 242 to explore an extreme option. This is a complete new AC system installation from Classic Auto Air. I also spent the time installing Dynamat while the interior was out of the car. It was a LOT of work, but overall a good project.
I created a new web page all about the new AC conversion. CLICK HERE!
|Improving the Charge with a Bigger/Better/Badder Alternator
Dealing with a Cracked 240 Dash
Here's a VIDEO: https://www.youtube.com/watch?v=ksmMu0wwhuY&feature=youtu.be
Other threads to read:
Rear Wheel/Tire FENDER CLEARANCE
for your 240
This pic below was the final result of my 242 after the above inner fender trimming and there is zero rubbing, even when bottoming out the suspension.
When I was shopping for wheels to replace the Eikers, I knew I would need to concentrate on something with more offset than the Eikers, since I would need the extra room to add an adapter behind each wheel. I eventually settled on wheels that were 7.5 inches wide with 35 mm POSITIVE offset.
The adapter maker I chose was http://www.motorsport-tech.com.
The minimum thickness they will make is 15 to 20 mm. I went with a 20 mm thick front adapter.
Now draw yourself some diagrams if it helps you visualize all this.
Here's a good Turbobricks discussion thread with related info: https://forums.tbforums.com/showthread.php?t=339645
Turbobricks Wheel Guide: https://forums.turbobricks.com/showthread.php?t=72501&highlight=wheel+guide
HUB-CENTRIC versus LUG-CENTRIC
It's important to decide if you will be using a spacer or adapter that is either HUB-CENTRIC or LUG-CENTRIC.
Hub-Centric means that the center raised lip that fits into the wheel center is present and will keep the wheel centered before you lighten the lugs. It means that the weight of the car is supported by the hub.
Lug-Centric mean no center lip is present and the wheel must be centered using the lugs. It means that the weight of the car is supported by the lugs. There are many generic spacers on line that are Lug-Centric.
Here's a TB discussion for you: https://forums.tbforums.com/showthread.php?t=349054.
Steering Wheel Hub for the 240
Installing a Momo (or similar type) steering wheel in your 240 can really improve your driving experience. It gives you lots of options for choosing a stylish or sporty steering wheel in a variety of sizes.
You probably already know all this and luckily for you, that's NOT what this article is about.
V Belt Sizes
Information on factory 240 accessory V belt sizes used to be easier to find, but it seems to have mostly disappeared from many useful sites.
I put this info together many years ago for my own 240 uses. I thought I would share it here.
Here's a PDF printable version of the below table: https://www.davebarton.com/pdf/240_V-Belts.pdf
240 Headlight Switch Plug Problems
So here's the formula needed to swap in a newer headlight switch and plug.
1. White wire from old plug goes to position 1 in new plug.
2. Yellow wire from old plug goes to position 5 in new plug.
3. Red wire from old plug goes to position 4 in new plug.
More information on adding a RELAY to upgrade your early 240 headlights can be found here:
MORE VOLVO BULB REFERENCES
Matthews Volvo Site Bulb Guide: https://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=61483
Other 240 interior and exterior bulb info in this Turbobricks thread: https://forums.turbobricks.com/showthread.php?t=283706
iPd Bulb Reference: https://www.ipdusa.com/techtips/10096/what-light-bulbs-fit-my-volvo
Volvo has owner's manuals going back many years (bulb info is in "Specifications"): https://www.volvocars.com/us/own/owner-info/owners-manuals
Gentex Rear View Mirror UpgradeAdding a more modern mirror for your 240 on the CHEAP.
with Auto Dimming, Compass and Outside Temperature.
|Guide for Crimping
I've put together a page with instructions for crimping and assembling typical open barrel or EFI crimp terminals and connector housings.
|Hydraulic Clutch Info
Page for your 240
I have a pretty heavy clutch in my 240. Back in 2011 I got tired of stretching, adjusting, stretching and then snapping clutch cables, so I installed a hydraulic setup for the clutch. I recently updated the master cylinder from the Volvo unit to an aftermarket one and created a web page to help keep track of the parts and information for others to see.
Here's the new page below:
|Mounting Driving Lights
on your 240 without Drilling your Bumper!
|Making a Custom Cup
Holder for your 240
We all know our beloved 240s never came with cup holders. There have been a number of cup holder projects in the internet over the years. When I saw this one in the Turbobricks forum, I felt it really needed to be shown. The thoughtful design allows it to be securely anchored over the e-brake handle, using the e-brake handle button to help pin the front against the shifter hump. It's a nice design feature to keep in mind when you build (or adapt) such a thing for your car.
See more photos and dimensions here: https://forums.turbobricks.com/showthread.php?t=328054
G80 Locking Differential (from a 700/900) into
Common Corroded Ground Points (and power
connections) In Your 240
I hear about strange intermittent electrical problems from frustrated 240 owners quite often. These problems occur so often because of a few good reasons . . . .
your 240 Taillights (Tail Lamps)
|Quick Fix to get your
240 Taillight Bulbs to Work Again (using aluminum
If you have the above circuit board issues and don't have the time or patience to hard wire your bulbs (above), here's a quick fix. Thank you to Michael Yount for offering this solution.
Simply cut some small pieces of aluminum foil and place them on your circuit boards as shown in the photos. Use some hobby tacky glue to keep them in place. They will help bridge the bulb holder circuit if you have worn out circuit boards.
Lowering Your 240
Should you change the ride height of your 240?
That's a question that comes along often enough. You have to decide if you like your car at the original ride height (cause you drive in floods?) or if it looks better to you a little lower. Sometimes the road conditions in your area will help you decide, since lowering a car means a more firm ride and less undercar clearance. If you decide you want to lower it, here are some options to consider.
Sport Springs: Most sport springs that are available (iPd Sport Lowering Springs being the most popular brand) will lower your 240 about 1.5 to 2 inches. Other spring companies offering 240 springs: B & G Suspension, King Springs (Australia), Classicswede.co.uk (UK).
The ride will be a little stiffer, but it will be very important to use good struts and shocks that will be able to control a stiffer spring. Bilstein HD shocks or Koni adjustable shocks are a pretty good match to this type of spring.
Adjustable Coil Suspension (Coil-overs): These are nice if you can find them. They offer a wider range of adjustability allowing the use of a variety of coil stiffness and adjustable ride heights. Occasionally there are people who produce kits in small quantities for 240s. Usually not though. If you're handy, you can build your own set.
Here are some good resources:
240 Coilovers: The Kyote Way
DIY 240 Series Coilover Instructions
Search the Turbobricks forum for more.
Cutting your Stock 240 Springs:
There are people online who will scream at you to never try this! I think it's because there are more failures from inexperience than great successes. The key to getting it right is experience and getting it right is definitely possible.
(Restored page at https://www.240turbo.com/tuff242_lowering.html)
And for more info, you can read the following threads, particularly the posts from Tuff240, author of the above page, who has more experience cutting 240 springs than anyone I know.
This is the best information I know on this subject:
Badass HEADLIGHT HARNESS using Relays
This is a good project for anyone with any older Volvo, especially if you have or want to to upgrade to brighter bulbs or headlights.
For the best info I know, read Daniel Stern's page on this subject. He also has several useful diagrams for designing and building your own relay harness.
Here are some Volvo specific diagrams that have been available on-line for many years. These use the same principles:
UPDATE 2018: Wagonmeister is now offering ready made 240 headlight relay harnesses.
the Mysteries of the 240 Headlight Step Relay
And Test Procedure.
This relay is rather special in that it has a LATCHING function. A latching function is where you can click and release a momentary button or switch (such as a high/low beam stalk) and the relay will LATCH (or lock) in the ON or OFF position until the switch or stalk is clicked again. For this Volvo relay, one click latches it "ON" and another click latches it "OFF." I have created the diagram PDF for anyone who wants to better understand how these relays work.
I have also added a test procedure on page 2 if you think you might have a broken one.
|How to Substitute
to ELIMINATE your Volvo 240 Headlight Step Relay
Understanding and Dealing with a Volvo Bulb Failure Sensor
|MOST SIMPLE SOLUTION
Bypassing a Volvo Bulb Failure Sensor
Making some simple BYPASS LEADS for a Quick and Easy Fix.
If you don't feel like going to the trouble of modifying a Bulb Failure Sensor internally, there is a simpler way to bypass these circuits without using a sensor. And I don't mean to suggest cutting off the 15-pin plug and splicing wires together (which of course you can do if you like). A better method, with no barbaric butchery, is to assemble some simple crimp terminals with a few short pieces of wire. Then insert them into the female 15-pin connector, respective of the bypass diagrams shown below As it turns out, this connector uses fairly common 3.5 mm bullet terminals. So all you need are some male bullets and wire and some heat-shrink tubing for insulation. Coincidentally, these 3.5 mm male terminals are available cheap on-line or also in my Harness Parts Page HERE.
In the photo below, you can see how these bypass wires will look. The configuration is different for different sensors, so pay attention to the diagrams.
|Modifying your Volvo using
I'm putting this here because having an understanding of simple relay functions can help any DIY Volvo mechanic in so many places for your car projects. Many of the suggestions in this 240 modification page rely on relays. Not too many years ago my relay knowledge was limited to installing a pair of fogs lights. The internet has helped a lot in this area and most of you can now be really successful with relays.
This Relay Guide is not Volvo specific, but it's a great resource for expanding your general auto relay knowlege and offers some interesting diagrams.
https://www.davebarton.com/pdf/RelayGuide.pdf (3.3mb PDF)
Here are some other pages with more relay explanations and configurations:
http://www.danielsternlighting.com/tech/relays/relays.html <<< And this is the best site I know for improving your auto lighting with added relays.
If you know of any other useful resources that would be a good fit here, please email me.
(Blinker) 3-FLASH UPGRADE for your Volvo
using a VW/Audi Komfort Blinker Relay
240 M46 Overdrive Wire Harness Design, Construction, Mods
240 Auto Transmission Overdrive Wire Harness Design and Construction
Since I did the above M46 diagrams I thought it would be good to illustrate how the 240 auto trans ORANGE and WHITE overdrive relays work. There is almost no difference in the relay circuits between these two relays. They are essentially interchangeable, EXCEPT that the OD light on the dash seems to come on opposite of when it's supposed to when the other relay is installed.
|Upgrade the In-Tank Fuel Pump in your 240
with a Larger 740 Turbo Pump
The Bosch in-tank fuel pump found in your 240 Turbo will be the same pump used in all 240/260 models from 1976 to 1984. It's very small and while it will provide adequate fuel to the main pump for a non-turbo Volvo, it has been considered by many to be too small for a turbo motor with any increased engine performance. The Volvo part number for the original 240 in-tank pump up to 1984 is 1276330. In 1985, that part number changed to 3507436, which was used through 1993.
The used 740 Turbo pump I used for this conversion, which was used in 1986 and later 700 and 900 Turbo models (and 960), is PN 3517845.
I got mine from a salvage yard.
This pump retails new for between $150 and $200. It is also widely available in salvage yards for a lot less, although you should be cautious, because some pumps found in salvage yards may be dead. I chose to install a used pump from a salvaged Volvo due to cost.
A good tool to bring to a salvage yard to test electrical parts like this is a drill battery.
If you need to test a pump, do it very briefly... only for a second. These pumps are not designed to run dry and it can damage them quickly.
Here's a video that might help.
G E T T I N G S T A R T E D
MORE USEFUL LINKS ON THIS SUBJECT
|Adding a Large Tachometer to your Volvo 240
in place of the Large Clock
Fuel Line Repairs
Volvo used semi-rigid plastic fuel lines on all 200, 700 and 900 series. Probably a lot more models, but I'll deal mainly with cars made in the 1980s and 1990s for this article.
Special thanks goes to Roger Brown of Pueblo, Colorado for the photos and details from his own fuel line repair. The photos below are of 740 fuel lines, but the principle is the same for 240s.
You'll find that the plastic hoses used in these cars are fitted to fairly standard brass or steel barbed nipples. Volvo fitted them when the hose or nipple or both are heated to a point the plastic becomes more flexible. Removing these hoses from existing nipples can be difficult and you may find that cutting or slitting them at the barb is the best treatment.
Here's a video of the general idea.
Small 52 mm VDO/Volvo Tachometer to your 240
|Fixing Bad 240 Driver Door Lock
I have seen a fair number of emails like this one:
"I own a 1993 Volvo 240 Sedan. It has about 100,000 on it and runs beautifully. The only problem is that the central locking system seems to be malfunctioning. It makes a fast clicking sound when driving and sometimes goes up and down when one tries to unlock the other doors from the drivers side. In the past two days the battery died due to something being left on. I pulled the #8 fuse (courtesy lights, clock, trunk light, glove box light, central lock system, power antenna, radio) and today the battery was fine."
This is an extremely common problem that literally affects ALL YEAR 240s equipped with CENTRAL DOOR LOCKING.
How do I know this problem is common in all year 240s? Because when I discovered this years ago i spent time at junkyards pulling off door panels on a lot of 240s up to the 1993 model year. They are all the same. All had BAD WIRES!
The problem is old, flaking wire insulation inside the driver door. Specifically, the wires going to the key lock switch ("F" in the diagram shown at left) and also the door lock plunger switch ("A" in the diagram shown at left). It should be pretty obvious once you pull off your door panel and look closely at these wires. The insulation on these wires will crumble and fall off, allowing the wires to short. This causes the rapid lock-unlock to occur randomly. And when the car is parked, the shorted wires may allow the locks be stuck in UP or DOWN mode, which can drain your battery in a few hours. The solution is to cover the bad wires with heat-shrink tubing, liquid electrical tape, etc., or cut them out and crimp or solder in new wires. You will probably only have to do this to about 8 inches of wires, but keep an eye out for more than that.
Here are a couple good threads with more photos:
Dealing with the Temperature Compensation Board in your 1986-93 240
||Center Cap Labels/Overlays
||240 Black Door Vinyl
|240 Alternator Mod Page
||240 Power Mirrors- Switches
||240 VIN Decoding
||240 Fuse Panel Page
||240 Lowering Page
||Fuel Pump Relay Mods
||240 Step Relay Elimination
|Used Parts & Stuff
|240 Gauge and Electrical Diagrams||Limited Slip Read Ends||Yoshifab Catch Can Install||240 Mods and Fixes|
|Side Marker Lights||Gentex Mirror Upgrade||Yoshifab Drain Tube Install||Modified 240 Favorites|
|SoCal Salvage Yards||Unleaded Racing Fuel||B26FT Stroker||Dave's 245 Spec Page|
|240 Big Brakes||240 Dash Top Gauge Pod||Cadillac 4-Note Horn Install||Vacuum Diagrams|
|4 Speed Fan
||Texas Volvo Meets
||Mojave Road Trail Page
||Volvo Meet Photo Albums