[mranth]

I bought new fuel and temp guages for my 79 CJ7. Installed them both and neither work. I've done the ohm test on the guages S to I, etc. And everything test good. I have 12 volts going to red wire on the fuel guage, fuel sender is reading proper ohm readings, Jumper wire is reading 5 to 8 volts, and Temp sending unit is reading properly. I ran a ground wire to the back of the speedometer cluster to one of the 4 mounting bolts. I can get the temp guage to read instantaneously if I pull the Ign. fuse and pop it back in. It will read and drop right back done to cold. What else could it be?
Thanks for your time.

-Mark

[scottymac62]

You stated that you have a ground wire going to the back of the speedo. Have you checked the continuity for that ground wire? You should also think about running a dedicated ground wire from your fuel sending unit. More times than not, these problems usually boil down to bad grounding.

[John Strenk]

Originally Posted by mranth

I bought new fuel and temp guages for my 79 CJ7. Installed them both and neither work. I've done the ohm test on the guages S to I, etc. And everything test good. I have 12 volts going to red wire on the fuel guage, fuel sender is reading proper ohm readings, Jumper wire is reading 5 to 8 volts, and Temp sending unit is reading properly. I ran a ground wire to the back of the speedometer cluster to one of the 4 mounting bolts. I can get the temp guage to read instantaneously if I pull the Ign. fuse and pop it back in. It will read and drop right back done to cold. What else could it be?
Thanks for your time.

-Mark

This is odd. I havn't heard this symptom before. Hmmm.... you said the temp meter is working correctly then you say it drops out when you pull the fuse and put it in? Did you mean the fuel gauge is behainving this way??

only a couple of things I can think of at the moment.

First is the winding and wiper on the sending unit is heating up and moving breaking the connection to the gauge. Doing an ohms test with so little current will not cause it to heat up and show good when cold.

Second would be a poor connection that fails when current is passed through it. Could be ground or terminal lead causing this.

How to test this theory would be fun. Using a test light made up of a tail light, see if the sensor wire flashes at the sending unit connection. and see if the gauge moves up when the light is connected.

See if the ground wire flashes on the sending unit also. It shouldn't.

[mranth]

The temp guage will read and then drop off to cold once I insert the fuse. It is very quick and I don't even know if it is reading properly on the guage. The sending unit will read correctly as I start the engine and it warms up.