VCCA Home Forums GENERAL DISCUSSION General Discussions Gas Tank Sending unit

I just did my 1935 Chevy master deluxe gas tank and sending unit. When I put the gas in all the way, full and red almost empty so I accidentally did something backwards on the sending unit. I was wondering is there any other way to fix this besides taking the tent down, does anybody also know what the two connections on top of the sending unit or four if I flip them around with my gas meter go back to normal or does one pacifically go to another one. I did grounded to the car. Any suggestions would be very appreciated. Thank you so much.

. Your stock 1935 Chevy only has one connection to the sending unit but the tank must be grounded. If it reads full all the time, attach a ground wire to one of the five screws that holds the sender in place. If it reads empty all the time, the sender wire is grounded. For more info read <http://home.znet.com/r1937/Fuel.htm>.
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. Lou .

If it's working but working backward as you describe reverse the wires on your gas gauge. If the tank wasn't grounded it wouldn't move at all with the addition of gasoline. According to the wiring diagram the gauge terminal closest to the ignition switch is the one connected to the switch.

It's OK to switch the two wires behind the gauge around and it won't cause any spark or anything. I do remember, I put one black ground wire just in case the tank wasn't grounded on one of those screws and grounded it to a bolt. And then the other sending unit wireless in the center that went straight to the gas tank. I just don't know burn anything out or calls any type of spark any direction or advice would be appreciated. Thank you.

Glad you got it figured out. Rereading my post I don't know what I was thinking but I clearly confused the gas gauge wiring with the horn circuit. For future reference I fixed my error. Sorry for any confusion it may have caused.

I haven't figured it out yet but I just put the 14th of gas and it went all the way to the E I don't understand what happened. I went in brand new if I flipped two wires behind the desk on the gauge I don't want to spark any contacts in my allowed to do that ? Because I thought the other one has power when I turn the key, it moves

Sorry for the confusion on my part. I suggest that you need to get back to the basics and use an organized troubleshooting approach. Randomly changing wires is obviously not solving the problem.

Do you have a wiring diagram for your vehicle? That is where I would start. Get one and trace each wire that is part of the gas gauge circuit end-to-end. Do a continuity test on each wire and make sure that none of those wires are shorted/grounded. Then confirm which wire is the hot wire that powers the circuit.

There is one other key test I do whenever I am working with a fuel gauge circuit. I always test the sending unit out of the tank to make sure the movement of the float arm will move the gauge needle properly. I do this before I install the sending unit into the tank.

I connect the wire from the gauge to the terminal on the sending unit. I connect a jumper wire from the sending unit housing to a good chassis ground. Then I turn the key on and move the float up and down while I (or someone else) watch the gauge.

That test has saved me a lot of time and grief when there are issues after the sending unit was installed. If the gauge worked correctly before I installed the sender then I knew the problem was related to the installation or something in the tank. In one case we determined that sending in unit was incorrectly grounding itself upstream from the rheostat. In another case we determined that the cork float was defective. It was so saturated with gasoline that it would not float above 1/2 of the tank depth even when the tank was full. Also it hardly registered until you have the tank at least half full.

A few points of interest. As long as the gas tank is grounded (and you can check that with an ohmmeter/multimeter) One lead on the tank and one on the chassis. Should read 0 ohms, then the sending unit will get its ground through the sending unit screws. No ground wire necessary. That too can be confirmed with the ohm meter. Note: This might not be the case if your tank is a rubber bladder but with steel, you'll be fine.

You can check the gauge from the sending unit just by either lifting the wire off the unit or touching the wire to ground. Off the unit should show full at the gauge and that same wire touched to ground will show empty. This proves that whatever the issue, the problem is NOT in your gauge.

There is a great YouTube video explaining the process. I believe it's on a 60 something Chevy truck but they all work the same. It was very helpful for me as I too thought I might short something out or make a spark and blow myself up. But not so. Give it a try.

And final point... the problem is almost always the sending unit. I fought with my old one to maybe get it to work OK to save a buck or two. Big mistake. They're cheap and plentiful, just replace it.

I agree that the simple “touch the sending unit wire to ground” is a great troubleshooting test. I also agree that in most cases the issue is the sending unit.

However in this situation the original poster states that after putting in 1/4 (I think that is what he means by 14) tank of gas he still gets an empty reading.

I may have missed this but is this a steel or poly tank installed in the car? We installed a poly tank when we did ours so we never had to worry about rust. Downside is that we did have to run a ground wire for the sending unit to make the gauge work.