The Stovebolt Site Forums The Shop Area The Electrical Bay 1954 fuel gauge woes

I have a 54 chevy 3100 that I recently bought all new fuel system components for. My problem is the gauge is still not reading. I have wired everything correct to the diagram and still not showing anything. The gauge shows 12vdc with everything hooked up outside the tank, but as soon as I drop the sending unit in the voltage at the tank drops to 1.25vdc. Any help would be greatly appreciated, this has had me stumped for a couple of weeks now

also should add that whenever i check ohms at the tank with everything disconnected (just sending unit in tank and ground) it shows 30 on my multimeter. Could this mean that I have a hot wire touching the frame somewhere and its causing me to have a bad ground?

First... Welcome to the forum.

Are you saying your taking a voltage reading at the tank sender unit?

Your Ohm reading at the sender sounds correct only if your tank is full.
Try Pulling your sender and testing it. Should read 0 empty and 30 full


The most common problem is a bad ground at the gauge cluster. I made this mistake myself.
The gauge must be grounded to the cluster.

Also check that the sender is grounded. On my 50 I ran a wire from the sender and it is grounded to the bottom of the Cab.


Good Luck

Yes I was taking a reading at the tank sender unit.

Glad to hear the ohm reading is correct.

Where did you ground the gauge to the cluster? I thought it only took the wire from the ign side and one continuing to the sending unit...?

The sending unit is indeed grounded to the cab as well

Thanks for all the help

If it’s a new gauge there should be a metal plate on the back.

Here is what mine looked like.
...pic...
(yours will look diffrent being a 54)

That metal plate on the back has to touch metal on the housing. Often times we paint our housings losing the ground.

If that ground is good you will have more troubleshooting to do.
Good Luck

Not only that, if it is any way similar to my 49's, if the gauge moves inside the housing at all, you can get a short causing burnt wires (done that) or a bad ground. The 4 gauges in the cluster have individual circuits inside and use the case as a ground. The wire posts protruding out the back of the cluster also hold the circuit in place.

This is great info to have! Thanks guys, never heard anything about needing it grounded so ill run a wire to ground it while everything is out and hope that this is the problem!

Number one cause of gas gauge problems, as said, is bad ground. Ground Battery to eng, eng to body, body to frame, sender to frame, gauge to suitable dash spot. ALL grounds have to be bolted to CLEAN metal. Use those grounding "digger" washers. Your whole system will run better. I assume an AD gauge is grounded? I know about TF only.

patrickm,

The 54/55 gauge is a little different from earlier gauges: here are a few photos but the principles-of-operation are the same.

As stated above above, bad grounds and no grounds (resulting in a needle "pegged" to Full) are common problems. And, unwanted grounds can also lead to problems.

Look at the two photos at the link:

1. In the uninstalled (off) gauge photo, look at the ground metal between the posts and note a circular metal?-thing in the middle, and note that neither post is connected to the ground.

The gauge-housing is grounded and it is usually a good ground; however, make sure the gauge attachment-nuts and where they touch the dash are good/clean-metal.

NOTE: when the gauge is installed into the gauge housing, neither the fuel-gauge posts nor that circular thing between the posts touches the housing.

2. Look at the installed gauge and notice two things: 1. the red label indicating "sender connection" is on the sender post (and must not be connected incorrectly); and, 2. there is a piece of cardboard that goes on each post and in-between the posts - this is to assure that you do not accidentally touch the wrong lead to the wrong post.

The most important ground for the gauge/needle circuit is between the sender "cap" and ground. For diagnosis/testing purposes, I sometimes run a "ground-confirmation" lead from a sender cap nut/screw to the frame or some other good ground (to make sure that a bad reading is not due to a bad sender ground).

Good luck,

Sorry to jump in but on my 46 do I run a ground wire from the sender to the frame? Or is there another way? Thanks in advance.

Dan

Yes, sender to frame.

I agree with TC, my opinion is you need a permanent wire from one of the sender mounting screws directly to the frame, always. Tanks are isolated because of the mounting pads and the ground is therefore left to go thru the straps and strap bolts and maybe a little thru the lines. NO GOOD! (TF burbs)

Thanks for the added info gentleman. I finally got to go take a look at it again today and now this is what I am seeing:
The gauge reads all the way past full/pegged out when the ign is off, whenever it is on the gauge reads just past full. Could this be a bad ground somewhere else on the frame? I know for a fact all the wiring is straight, the only one that I havent replaced is the sending unit to the gauge... Also the sending unit is currently grounded to the cab, should I move it to the frame?

Thanks again,
patrickm

patrickm -

Is your gas gauge a 12v reproduction? I installed a 12v gauge from The Truck Shop on my '54 a couple of months ago and like yours, it does not return to EMPTY with the ignition off. Since the gauge is located at 2:00 on the gauge cluster, gravity sometimes pulls the needle past full with the ign off as you describe. Otherwise, it works fine. (FYI - The 12v gauge is manufactured differently than the original 6v gauge. Three coils instead of two).

This Fifth Avenute Tech Tip seems to describe your problem:

6) If dash gauge reads, FULL when tank is known to be only half full the wiring between the tank or the sender is bad. Ground the gas tank sender terminal using a jumper wire, if the dash gauge still shows full there is bad wiring between the dash gauge and the tank sender. If the dash gauge goes to empty, the gas tank sender is defective.

This is the link to the full article.

I made sure that everything is grounded well.
- bare metal on the inside of the gauge cluster where it contacts the back of the gas gauge
- bare metal on the outside of the cluster where it contacts the mounting nuts,
- jumper wire from a good ground to one of the screws that attach the sending unit to the tank.

FWIW - I tested my gauge before I installed it, however, it only read EMPTY after I installed it. I found that I had over-tightend the terminal on the sending unit that held the rheostat unit to the round body of the unit. I had collapsed the insulation or maybe rotated the rheostat unit to allow it to touch the body.

Good luck,

Good stuff from LonnieC. My 2 cents: Run separate "test" wires. One from the sender mounting screws to neg batt post and one from sender center tap to gauge. Just use some good wire you have and let it hang loose on the ground, or whatever, just to have a direct bypass of all existing wires. That's how you trouble shoot electrical/all problems. Isolate. Isolate, Isolate. This will tell you that you can eliminate wiring as the culprit and move to sender or gauge or gauge wiring as the problem.

It's not a truck but I'm working on a 52 chevy sport coupe with the same problem. The sending unit stud on the gauge is showing fully grounded with wire unhooked. I'll have to pull it to see whats causing it.

It you look at the back of your gauge you will see the metal plate. It must have good contact with the metal housing. If you cleaned up and repainted the housing make sure you sand off any paint where the gauge will mount so you have bare metal contact with the back or your gauge.

Image of back of gauge:
http://1954advance-design.com/Web%20images/1954%20fuel%20gauge/rear%20posts%20off.jpg