Hey everyone,
I have a 79 Ranchero 500, and im having a few problems with my gauges. My engine temp gauge doesnt even move, its stays at C. My fuel gauge is always shaking. Finally, my spedometer bounces like CRAZY when i accelerate. Im in the middle of restoring the chero, so if anyone knows how i can fix this, that would be great. Im guessing it could be a short, because i saw that under the steering wheel, some wires are taped with electrical tape. If you know how to help, please tell me! Thanks!
Danny

 

How to diagnose Sending unit/gauges problems.

To check the gauges with the key off:
Take the connector for the oil pressure sending unit off
put a cotter pin it, now attach it to a good ground,go back and turn the key to ON > If the gauge pins to the high side the gauge is good.

Now do the same with the temp sending unit.


If the gauge DOESN'T pin, there is either something wrong with the gauge,wiring,or IC V reg.

To check the IC V.Reg with key ON:
Take a test light and attach it to the sending units wiring.
You should have a PULSING light.
If so, the IC V. reg is Okay.

If Not,either the wiring is bad or the V reg. is bad.
The IC V.reg is located on the back of the Instrument cluster.


So,If you have a gauge that Pins and a Connector that Pulse flashes : the problem is with the sending unit.

Check the S.U. for teflon tape wrapped around the threads.
If so,remove it and check it again for gauge reading.

Alwats use the proper sealant for sending unit threads.
Teflon tape is insulator
You need a conductor sealant.


Oil pressure change :

Usually from a worn oil pump or from the expansion of the cam & crank bearings causing the pressure to lesson when heated up.