The Stovebolt Site Forums The Shop Area Engine Shop fuel gauge puzzle on 1950 truck

I've just replaced the entire wiring harness on my 50 chevy, everything works except my fuel gauge and it was working including the fuel sending unit prior to replacing the harness. Here's my problem: When I turn the ignition key on, the fuel gauge needle moves up to the full position, yet my fuel tank is empty. I've removed the fuel gauge from the gauge housing and attached my two wires one is from the ingnition the other goes to the fuel sending unit and the needle stays on empty. When I mount it to the gauge housing the needle goes to full position. It almost like I got a short when the fuel gauge comes into contact with the housing but I never removed the gauge from it's housing prior to this and it worked. Should there be an insulator of some sort at the base in between the fuel gauge and the housing so they don't come in contact with each other? There was none present prior to removing it from the gauge housing. The other thing is that if I don't let the fuel gauge touch the housing the needle stays on empty eventhough I've moved my sending unit (float) manually (it's removed from the tank)up and down. There's no motion from the fuel gauge needle. I also tried putting my ohmmeter on the sending unit (which worked fine prior to the rewiring) to check for resistance should I not read something when I move the float up and down. Is there anyone out there that has an answer to this problem. I've spent five hours on this and lost for answers. This is a six volt system and I wire by ignition wire to the F side of the fuel gauge the other (E) goes to the sending unit.

My new fuel gauge and sending unit did the same thing. I finally figured out the power wire was shorted to the gauge. It went over full and would not read anything. Make sure you have an insulator on the two connections and the sending unit needs to be grounded. I got my answers by serching this site and on the old car manuals site. it works fine now.

Thanks I do have the original insulators on the back side of the gauge housing and did check for short none there and my sending unit is grounded, but I will check again to make certain.

At the sending unit, take the sensor wire loose from the sending unit.

Take a test light and ground one end of the test light, then place the other on the sensor wire. Turn the switch on and see if the gauge still goes to full. If so, you may have an open wire between the gauge and the tank. The gauge should move some towards the empty (may not go all the way) because the bulb in the test light will act as a resistor.
You can also do this same test at the back of the fuel gauge to help determine if the sending unit wire is bad.

Usually when the gauge goes to full then it isn't getting a good ground through the sending unit. Was anything painted while doing the rewire? May add a ground wire to the sending unit by using one of the mounting screws for the unit to place one end of a wire and running the other end of the wire to a good ground on the body.

When a fuel gauge behaves as you described (pegs to full when the ignition switch is on), you most likely have a good gauge but you do not have a good gauge to sender/ground circuit.

Three possibilities:

1. broken (or, no) lead between gauge and sender.
2. bad sender unit
3. sender body is not grounded

The easiest way to test/diagnose this is to attach a lead-wire from the sender side of the gauge and attach that lead to a god/clean ground. The gauge should drop to zero.

Then run a long lead from the sender side of the gauge to the input side of the sender in the fuel tank. If the gauge does not read properly, then run a ground lead from an attachment bolt on the sender/tank to a good ground. If this does not give a correct reading, then remove the sender and "bench test" it.

DJRoy

Here are some photos to go along with the good advice that you received from previous postings. I snagged most of them from albums by DADS50.

> Gauge-to-Housing Ground Photo by DADS50. This is where the back of the gauge should ground against the inside of the housing. Sand that spot on the housing to clean bare metal.

> Fuel Gauge hookup back of housing Photo by DADS50
> Insulator on back of housing 1 Photo by DADS50
> Insulator on back of housing 2 Photo by DADS50
> Insulator on back of housing 3 my photo
> Ground on sending unit Photo by DADS50
> Sending unit grounded to frame Photo by DADS50 The ground wire can be attached to any place on the frame that will be a good ground to the neg post of the battery.
> Ohmmeter test of 30 ohm sending unit Photo by DADS50
> Bench test of 30 ohm sending unit Video by DADS50

> Good info from DADS50
> Fifth Ave Tech Tips
> ChevyTrucks.org Troubleshooting Your Gas Gauge

Great info! My gauge has never worked, and as soon as the weather breaks, i'm going to rip the dash apart and see if I can fix it. I suspect a bad ground from the gauge to the housing.

Thanks guys for all the good advice, it turns out the sending unit was no good. It was the original and after I open it up the resistor band inside was broken. I ended using a test light to pinpoint the problem, thanks Roy that was good advice. What through me off was that it was intermittent. Ordered a new one can't wait to put it in. PS: Taking that gauge housing off the dash is a pain in the butt.

hi all, to bad most of lonnie's links dont work anymore..
im rebuilding my instrument cluster and looking for info on the shunts and proper connections. any help?

You should start a new thread, with details to your particular questions.