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I recently repaired the sender in my 1995 940 sender unit. Below is the write-up I did for Steve's FAQ. It hasn't been edited yet, but this worked for me
Feel free to contact me if you have additional questions.
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My Fuel Gauge Doesn't Work [Bad Fuel Level Sending Unit Contacts]
From Nathan Babcook (RepairmanJack)
Fuel Gauge failure seems to be rather common in 940 Volvos. I requested and received a lot of information before finally solving the problem. The Fuel Level Sending Unit and Tank pump assembly is a fairly straightforward design. There are not a lot of moving parts to break, and if you are careful about your diagnosis you can avoid having to "crack anything open."
Diagnosis Proceedure:
As discussed previously, be sure you test the gauge with a 1/2 watt 68 Ohm resistor. it HAS to be 68 ohms, 47 will not work! Nearly every radioshack stocks the 68s, they retail for around $1.00 for a pack of 5 (Part no. 271-1106) - check the radioshack website before you head over, as the employees frequently don't know what they have in stock!
Be sure the car is turned off! Disconnect and "bag" the negative (black) battery wire (i used two zip-lock freezer bags) Also be sure you get the radio-activation-code - if you need it.
Find the sending unit plug and disconnect it (in the 1995 940 wagon it was a 4-wire quick connector located in the driver's side hidden compartment). There should be a Black, Red, Brown, and Grey/White wire. Note: the brown wire becomes a second grey/white wire in the where it runs to the sender unit itself - Nothing to be worried about! The red wire runs to the pump, the black is your ground and the grey/white and brown wires are your fuel level sending unit wires. [your wires may differ slightly in color depending on year]
Before you deal with the sending unit, be sure that your much-easier-and-cheaper-to-replace gauge is working. Bend ONE resistor into a "U" and insert it into the harness side wiring - one side into the ground (black wire) connector, and the other side into the brown wire connector (or grey/white, I forget, I don't think it matters). If your wiring harness and gauge are fine, the you should read approx 1/4 tank (after you reconnect the battery and turn the key to KPII). If you can't get this to give you a reading, suspect your gauge is at fault - a cheaper and easier fix - or that your wiring harness is at fault (see the gauge fault diagnosis in the FAQ)
If the gauge and main wiring harness is fine, then your fault lies in the sender or the wiring to the sender. Use a multimeter (one capable of reading small scales like 1-250 ohms is best). Measure the ohms between the two grey/white wires coming from the sending unit. If the sending unit is perfect you should get a reading between 2 and 131. If you get no reading (i.e. infinity - an "8" on it's side) then there is a problem with the wiring or contacts inside the unit and you'll have to pull it.
Diagnosing and repairing the damaged nickle-plated contact is discussed elsewhere. I found that in my original unit and a spare that I grabbed from a junkyard, the contact strip was perfect and undamaged.
Pull the whole sending unit. It's a bit of a pain, but not impossible. Unless you have $500-600.00 extra laying around, then give it a try - it wasn't all *that* hard. Once you have the unit pulled, drained of gasoline and dry, turn the unit over to be sure that the slide moves easily (you can hear the float inside the float canister sliding from top to bottom). If it doesn't then your problem is inside the canister (see "repairing the sending unit"). If it does move easily, you may not need to crack it open.
Break out your multimeter and measure the resistance again by touching your probes to the coils that stick out of the top of the float canister (hint: the two grey-white wires are sodered to them). Be sure you move the float up and down by turning it over and measuring it with the float at EACH end of the canister! If the coils and resistor contacts are fine you should get a resistance reading of around 2 at the top (full) and around 100+ at the bottom (empty). If you get a reading here, then you can assume that your grey/white wires are the problem. To check these wires, de-soder (or cut) the wires free from the coils (I marked one with a sharpie so that I could put them back if needed). After they are free, connect them to each other (twist or clamp) and measure the resistance at the plug-end of the connector. If the wires are fine, you should get a 0 Ohm reading. If not, then you'll need to replace the wires (good luck).
If the wires are fine, and the sending unit float is giving you proper resistance, then you can be fairly sure that the fault lies at the soder point.
The Repair
Clean up the wires an re-soder them to the coils. Be sure that you can get resistance at the plug end of the wiring. This worked for me. Although I'm not sure if it will hold up, I went ahead and installed some shrink tubing over the connectors as an added level of protection. if you can now get the proper resistance from the sender aparattus at the plug, you are in good shape.
Final Testing
Head back to your car and plug the sending unit into the harness (DO NOT put it in the fuel tank yet!!). Reconnect your battery and turn the key to KPII - BE CAREFUL!, when you turn the key, the pump should fire up and could make the unit jump, possibly falling and damaging it!!! It may take a few seconds for your gauge to respond to the repaired sender - particulalry if it's been at "E" for a long time, but you should be able to turn the sender so that the float "falls" to the top, this should make you gauge rise to "Full" (eventually). Be sure you let it fall to bottom and be sure that your "low fuel" light comes on. Repeat to verify your repair. If all goes well, you may have just saved yourself $500.00 in parts and more in labor!!!
Reinstall
Replace the sender unit/pump in your fuel tank (easier to get into the tank, but harder to get that rubber seal and locking ring on) It's not fun, but think of all the money you just saved!
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Six Volvos: all wagons.... 1972 145S, 1976 245 DL, 1983 245 GL, 1986 740 GLE, 1990 740 GL, now a 1995 940. Number 7 (a 1967 122S Wagon) is on the way.... Who needs a sedan, when you've got storage compartments in a wagon?
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