I was doing some work and thinking about a logical approach to it. Here's what I came up with:
1) is your Temp gauge working properly? If Yes then this means your 6V regulator probably works fine. If No then check that (see 2) below )
2) (independently) Put the DC voltage part of your meter on the output of the 6V regulator on the back of the dash (I want to say the wires are Green but you should check the wiring diagram). You should see it fluctate as it is going On and Off with the average being 6V (as your car is 12V).
If it is 0 volts all the time it is dead. Buy a new one
If it is 12V all the time it is stuck and also needs replacing. It will fry your gauges if not replaced.
3) Assuming the 6V power source is OK then move to your gauge. Disconnect the lead that goes to the sending unit (again see Wiring Diagram for colors). Briefly ground the post on the gauge out (with the key on Accessories) and see if the gauge jumps up to Full. If Yes then your gauge is probably fine. If No it is dead.
Wire things up as they were and move on...
4) Assuming your gauge is OK then move to the trunk and move the floor mat off the sending unit. Disconnect the lead to the sending unit and, with the key On, again ground out the lead to the sending unit. It should cause the gauge to jump up to Full. If not then the wire from the gauge to the sending unit is bad (broken) and needs replacing.
5) If step #4 went ok then move on to checking the sending unit.
a) remove it by rotating the retaining ring
b) cover the opening with rags and be very careful!
c) clean up the area where it grounds out to the body (paint, rust and goop may be found)
d) put your multimeter across it with the meter in Resistance mode and see if it has continuity. By "across it" I mean with one lead on the post the wire hooks to and the other on the metal cover (which is ground). Try different resistance scales. If it always shows an infinite number of ohms you have an Open circuit and the sending unit needs to be repaired or replaced.
e) if it does show resistance then you can simulate its action by reconnecting the lead from the car to its post and putting a jumper to its metal body and to the body of the car. (keeping away from the gas tank and still having the opening of the tank covered up for safety sake). Turn the key to Accessory and move the float arm around and you should see the gauge move back and forth from Empty to Full.
Now somewhere in all this, a step should fail and you can identify the bady component or lack of ground. But it is a linear circuit and by moving from front to back you should be able to identify your problem.
Please let us know what you find!
Once you get it working you can calibrate the gauge with instructions that Alexander on this site.
Last edited by JohnG : 12-31-2008 at 06:19 PM.