Propane to stock fuel gauge wiring

[TinnMann]

Hello all! First time posting on here but have read a lot of threads. I just bought my dream truck 70' chevy c20 longhorn and she needs some work.

One of the issues i can't figure out is the fuel gauge wiring, i have done many searches and still cannot figure it out. btw i am what you call an electrical dummy.

My truck is on propane and has a stock gauge cluster. Whoever did the conversion left a wiring mess btw. Can i wire my sending unit to the pins at the back of the fuel gauge? Kind of like i have some of them connected on the picture. or do i connect it somewhere on the wiring harness?

The pins on the back of the fuel gauge: top post closer to the passenger side (right post if you are looking at the face of the gauge) is the ground? The bottom post in the tank sending unit? and the top post on the drivers side goes to the fuse panel labelled fuel gauge?

If this is correct can i wire them straight from these posts or do i need to tap into the wiring harness or pin outs somewhere? Thanks in advance!

[VetteVet]

welcome to the forums. This must be a first. A new member that posts pictures in his first thread and even tells us what year his truck is.

The stock fuel gauge wiring is pretty simple but what you have is not what the stock gauge has for wiring.
If you look at the fuse panel you posted, you will notice on the left end there is a terminal labeled FUEL. This is where the sending unit wire from the tank goes.
It is a brown or tan wire and on the back of the panel is another tan wire that goes to the plug in the dash cluster to the no.4 pin. If you are wiring the fuel gauge directly then your sending unit wire will go to the bottom pin in the picture where you show a white wire going. Looking at the face of the gauge this would be the one on the right ( passenger side ).

The top terminal where you show nothing going, is the hot terminal for the gauge and also the hot for the temperature gauge. It comes from the cluster plug on terminal 3.

The other white wire you have on the gauge is going to the gauge ground, which is already grounded if the cluster is grounded.

If you take the sending unit wire off the gauge it should go to the far right to the 2:00 O'clock position.

If you ground that sending unit wire the gauge should go to the empty position, this is with the key on of course.

Lastly you want to make sure the tank is grounded to the frame and you have to be sure the tank sending unit is compatible with the fuel gauge. It should have a empty to full resistance from zero ohms to 90 ohms.

Hope this helps.

[TinnMann]

Thanks vettevet, I will post back if it works. The propane tank is old and needs a restoration/replacement for sure so who knows if the sending unit even works properly anymore. I need my wife's help when doing wiring because i am colour blind, which is one reason i don't like wiring haha so whenever she can donate time to help is when i will try to wire it

[Axle]

You can test the propane tank sending unit with a small pencil magnet (don't use a supermagnet). Remove the guage from the tank, and you'll discover it is just a disk, take the magnet and move it around the backside edge and see if the tank guage moves. Theres a magnetic float in the propane tank, which acts on the tank guage. After that, its traditional checking of wiring if the guage cluster doesn't function. I'd start with the splice to the factory guage wiring under the truck.

Alex.

[TinnMann]

Wont i lose the propane that is in the tank if i take that sending unit out?