The Stovebolt Site Forums The Shop Area The Electrical Bay fuel gauge always shows full

the fuel gauge on my 1951 3600 pick up always shows full, any ideas on what is causing this?
Thanks in advance!
Cadee.

If the gauge is working then you have an open or a bad ground between the gauge and the sending unit. Check the wire from the gauge to the sending unit. and check the ground at the sending unit to the cab. Then check that the cab is grounded. If that don't get it check in the Tech tips for more.

The level shown by your gauge is based on the resistance it see's in the circuit. With the gauge working properly a full tank has the float all the way to the top & the rheostat on the sending unit providing full resistance ~30 ohms. An empty tank would have the float at the bottom where the resistance would be ~0. Knowing that, a gauge that always shows full means the circuit is broken, full resistance. It could be a bad ground as noted by Steve or it could be a broken hot wire (as my '38 had). If you have a good ground and a good hot wire you'll need to look at the sending unit and/or gauge. You can check the sending unit with a multimeter.

Ok thanks guys for the tips...i will try them hopefully this weekend.
Cadee

My gauge was doing the same thing. Turned out the terminals on the back of the gauge were corroded/rusty and not making good connection. I cleaned with sandpaper and oiled the terminals and now it works perfect.

my gauge is always reading 1/4- 1/2. I have all new parts from sending unit to gauge. Gauge being the last thing I bought. ungrounded it moves freely spiking to full. Grounding it brings it back down between 1/4 and 1/2. Original gauge did the same and that was the last part I replaced in my trouble shooting. The sending unit reads 0-30 ohms on my multimeter. when I pulled the gauge out to make sure the needle wasn't stuck on the glass that didn't make a difference. working the float by hand doesn't move the needle either. any ideas here?

helps to state year Eric, some AD's apparently need a good ground to the gauge case - when working the sender by hand, did you have it grounded to the truck well? if moving the [grounded] float doesn't move the gauge, there's a problem in the wire from the sender to the gauge, have you checked continuity of it?

Bill

1950 3100. I ran a ground wire from the post on the gauge that connects to the sending unit to a post on the dash that the case mounts on. that brought it from spiking at full to the half indication. I've been frustrated and don't really remember what I had grounded when I worked the float by hand. I'll try that again and check wire continuity. thanks.

When checking the sending unit put the black lead of your multimeter on the case and the red on the positive lug.