The Stovebolt Site Forums The Shop Area The Electrical Bay Gas Gauge - Interesting issue

Hello all,

I hope you might be able to help me out. I have a rebuilt converted to 12V gauge cluster installed in my 49 suburban. The gas gauge has never really worked right, which I am suspected it's a gauge, but maybe you can help me confirm.

First question: My gas gauge reads full when the key is off, and when I turn the key to on, it reads just below half. Is it suppose to read full or empty when the key is off? It's a GMC gas gauge converted to 12V (I like the GMC color of the gauge better)

Here's what I've tested so far:

The lead to the left post of the gauge (from behind) reads 12V when key is on.

I have continuity between the wire on the right post of the gauge and the sender wire at the back connected to the tank

When I remove and ground out the sender wire from the sender and turn the ignition on, the gauge moves to that same position as always (just below half)

Thoughts?

Should this gauge read empty or full when there's nothing connected to it? I've removed both the power and sender wire from the gauge and it still reads full.

I believe that your "Full" needle position when the ign is off is a 12v thing.

I have an aftermarket 12v gas gauge from The Truck Shop in my '54. Gravity pulls the 12v needle down when the ign is off, so it falls toward and beyond "Full." The innerds of the 12v gauge are completely different to the original 6v gauge. The 6v gauge goes to "Empty" when the ign is off.

RE: reading 1/2 full with the ign on --
> Are you sure that the tank isn't half full?
> Possibly the float in the tank is sticking.
> Check to see if the needle is touching the face of the gauge or the glass of the cluster.

It takes my 12v gauge a few minutes to move to the correct reading after I fill the tank.

Lonnie. What do you mean the "F" position is a 12v thing?

I guess the sender could be sticking, but if I read ohms from the sender it's reading within its range. I should add fuel while reading it just to make sure

I will check the gauge maybe sticking itself to the glass

I mean that the aftermarket 12v gauge is constructed differently to the original 6v gauge - at least mine is - so it acts differntly to the 6v gauge. The 12v gauge does not return to Empty when the ign is off.

OK Lonnie - Thanks for the clarification. I'm wondering if I have a grounding issue at the cluster itself. Still trying to work through it.

The back of the gauge should touch the inside of the housing and ground to it. Make sure that the housing has clean bare metal where they touch. The nuts holding the housing to the dash should ground it, but scrape the metal under the nuts, plus scrape the nuts and the mounting studs to be sure.
< CLICK > For gas gauge troubleshooting tips.

Nice article! Thanks.

if the gauge reads 1/2 with the sender wire grounded it has to be a gauge problem

Bill

How was the fuel gauge converted to 12 volts?

I don't know - I have a call into the guy who restored them for me to ask him that very question. It looks like he used one of those replacement gauges from classic parts or a place like that.