The Stovebolt Site Forums The Shop Area The Electrical Bay Bench test for gas gauge

I have removed the sending unit and gas gauge and am testing them in the warmth of my basement. The sender works correctly but the gauge is giving me fits and I have some questions. When I test the gauge and the sender together, with 12v power to the E post, and out from the F post to the sender post, and a ground from the edge of the sender to the battery ground I get nothing. If the gauge was in the cluster housing it would be grounded to the dash, so should the gauge be grounded for the bench test also? If so, how? Is the metal strip between the gauge posts, with the little bump in the middle where the ground connects? And what do I connect it to, the same battery ground? to a pipe in the basement?
If I just connect the power and ground of an ohmmeter to the gauge set at 200 I get weird readings like 198 (on a 30 ohm gauge) and a spike to beyond full on the gauge. I'm trying to figure out if the gauge is broken or if I'm not grounding everything correctly. Any ideas are welcome, thanks, Steve

The back of the gauge should have a metal strip
That also needs to be grounded.

Ground it to the source your using


Here is an example
...click...

In that example I used that 12volt battery sitting on the bench

I used the - post as the ground

But the sender is also grounded, correct? Is it also grounded to the neg. battery post or does it need to ground to something else? Thanks so much for the info. I had broken the posts on the gauge by over tightening them and soldered them back on but I may have a small copper wire broken and / or the connection I soldered may have bled too far messing up the circuit. I hope I can determine definitively if the gauge is fixable or not, which is why I had asked if there is a gauge vendor that provides better quality gauges.
Also, thanks for the videos, they have helped. I got the loud turn signal flasher and am considering the LED turn dash lights.

Yes
Ground the gauge and sender to the same negative post on your source.
Your replicating the installation on the truck

By the description it sounds like your gauge is toast. But it's worth taking time to test it.



For the flasher I ended using a 12v PM 557. It's a loud click

I didn't like the beep the audible flasher gives

...12v flasher test

You are probably right about the gauge and I probably would have junked it if I hadn't gotten that weird spike to F. Probably means it gets 30 ohms but a gauge ground connection is broken or the F post is not getting power.
BTW, I fixed the sender by bending the little copper wire in the housing so it lightly made contact inside the housing when the float goes up & down. I hope this is reliable when reinstalled.

I was working on my 55 1st which is converted to a 12 volt this weekend. Assume the gas gauge is 6 volt as I never changed it. I took the following notes.

F post or post connected to sender

E post or post connected to ignition

Post to post resistance reads 29 ohms

F post to ground or outside of housing
27 ohms

E post to ground or outside of housing
57 ohms

Check for burnt or broken wires. Central rivet if loose can cause problem with the ground. Also need connectivity from housing to dash

I pulled the sending unit out of the tank while trying to figure out if the fuel pump was bad or I had a clogged line. While I had it out I tested it. An empty tank would read 7 ohms, whereas a full tank would read 35 ohms, at least for my sending unit.