The Stovebolt Site Forums The Shop Area The Electrical Bay New Fuel Gauge no reading!

Puchased new gauges for my 69 chevy. Installed then and they all work except the fuel gauge. When I turn on the power it moves from empty to just above empty. Origianlly I thought it was working until I filled up today and the gauge stayed put. If I disconnect the sender wire the gauge jumps to full. Is this a sender problem? My thought is that this is a compatability problem between the old sender and the new gauge, since the fuel gauge worked recently. Any suggestions?

Birdieall,

You have sort of proved that the new gauge is functional. With the key turned on and the sending unit disconnected, the gauge should swing to FULL...yours did! If you take the same wire and ground it to a shiny clean good ground, the gauge should swing to EMPTY...my guess is that it will. I don't know if you are doing this with the wire AT the tank, but if you are (and you should), it is also proving that the wire is good from gauge to tank!

That points the fickle finger of fate at the sending unit. It pretty simple..it's either the gauge, wires or sender, and the above test will pretty much rule out the gauge and wires.

Stuart

Tahnks Stuart! I'm headed to get a new sending unit.

I have a new tank and sender in my 50 1/2 ton (there when I bought the truck) it is 12 volt and I have a voltage reducer in line from switch to one side of gauge....mine reads full but when I run a jumper from the connection where the wire from the gauge goes to a spot on the tank it reads about 1/2 full which is about right...this don't make sense to me...or is it right? Virg
PS did I make this clear as mud

Virg,

It's a little bit muddy, so this might not make sense.

If the wire from the dash gauge to the sending unit is broken, the gauge will read full.

If the tank isn't grounded well to the cab/frame, the tank will read full.

If the sending unit isn't grounded well to the tank, the gauge will read full.

Is this what is happening?

Stuart

So what I'm doing is right...grounding the sending unit to the tank...will check to see if tank is grounded good to cab or frame...I think you answered my question atomarc...thanks..Virg

Atomarc,

Thanks for responding to this post. I am sure that I was not alone in being stumped by a gas gauge.

I am getting my 1942 truck back on the road. The gas gauge is 6 volt ( if they have a voltage ) with the stock sender in the tank. I hooked this up to 12 volts by mistake - have I cooked it? ( I say by mistake because the oil pressure gauge is a tube connection, the ammeter does not care, and I did swap the dash indicator light bulbs, but forgot that the fuel gauge needed some attention - until after I did this).

The needle on the gas gauge moves from one side to the other when jumped, but seems 'stuck' when hooked up correctly. Adding more fuel to the tank did not affect the position of the needle. I have a voltage reducer, but probably should have hooked it up prior to making the 12 volts live. Are they the besy way to switch voltage, or can the sender be altered to 12 volts?

Have I screwed the sender unit? Or the gauge? Can you recommend fix options for me? I have swapped in a 12 volt generator and it works well.

Thanks,


Stewart

Stewart,

Some folks say that hooking 12 volts up to the gas gauge will kill it, while other folks have run theirs on 12 volts for years...don't ask me why it works this way.

The system works using a variable ground to move the pointer on the gauge between two coils mounted in the gauge. The variable ground is supplied by the movement of the float in the tank across a wound resistor wire.

You can get a inexpensive voltage reducer made just for things like the fuel gauge from many of the vendors.

I would install the reducer in the power line ahead of the gauge and proceed with a little test that should troubleshoot the gauge, wiring and sender.

With the reducer installed and the key ON, remove the wire at the tank sending unit. The gauge should read FULL. Take the same wire, and with the key still ON, ground the wire to a good ground on the cab or tank. The gauge should swing to EMPTY.

If this happens, the gauge is good and the wire back to the tank is good.

If it doesn't happen, the wire could be broken or grounded, or the gauge could be NFG, or the gauge might not be grounded in the dash assembly.

If the test does prove good and the gauge doesn't read properly when connected again, the sending unit is NFG.

If you are industrious enough to pull the sending unit, and you have a ohmmeter, you should get a variation of near 0 to 30 ohms when you swing the float stop to stop.

If the gauge doesn't respond correctly during the little test, it could be the wires from gauge to back of cab. To verify 100%, you would need to attach jumpers directly to the back of the gauge (sending unit terminal) and find a good clean ground for the test. If the gauge is toast, it would have to be replaced.

I know this is a mini-novel, but it isn't often that two-Stu's/Stew's get to BS! Good luck!

Stuart

Stuart,

I borrowed a voltage reducer from a friend and tried the tests that you outlined. The cab is off the truck so this is easy to do. All new wires from sender to gauge were cleaned and verified.

The gauge is OK, but the sender is pooched. It is still in the fuel tank as it is very hard to get out in my application. I will wait until the winter to take that tank off to get at the sender.

Do you know if anybody fixes these senders?

Thanks for your assistance.


Stewart

Stewart,

I don't know anyone that repairs sending units. Sometimes, the sender can be cleaned up, the wiper cleaned and tightened against the wire and the thing will start working properly. Good luck.

Stuart