gas gauge test?

[NOT A TA]

I'm working on my 70 Firebird modifying the orig speedo gauge pod. After I got my mods done the gas gauge doesn't seem to be working. So I added gas and retried connecting the battery. Same thing. lights in pod work.Tried plugging unplugging several times the connector for pod. Dissassembled and reassembled pod and no difference. Anyone know of a way to bench test the gauge? I was afraid to give 12 volts direct from battery for fear of frying the gauge.

[Zee]

Use a VOM. The resistance should be 0-90 ohms depending on the float position. 7 times out of 10, the sending unit ground is corroded and just needs to be cleaned.

[NOT A TA]

Gauge worked fine till I messed with the gauge pod and printed circuit. I'm thinking I did something while modifying the pod and printed circuit to accept a tach and shift light setup. I'll try to check the resistance with a meter this morning but its tough to get at even with the steering column dropped a bit and the facia panel moved out as far as I can because of all the gauges, switches etc that are aftermarket stuff.

Is there a reading(resistance) I should get if the gauge pod is out of the car?

John

[HILROD]

As ZEE stated the wire from the gauge should have 0-90 ohms, depending on how much fuel it has in it. The other wire will have 12 volts to it. Usually if there is power to the gauge but no sender connected it goes to way past full.

[MrQuick]

I wouldn't recommend feeding the wire a full 12 volts. I've seen shorted wire do bad things around metal tanks full of combustibles.

The safest way to see if the system works is a ground scratch test. You can ground the input wire to chassis gound and see if the gauge works. You can work from the tank sender to gauge or visa versa.What ever is easiest for you. Keep testing closer till you lose the gauge.

My money is on the area between the gauge and the front seat.

[NOT A TA]

Thanks for the help, I fixed it tonight. I was thinking about your comments about the resistance of the sending unit. They're not SENDING they're RECIEVING power. So do the "sending" units for the "idiot" lights so when I was thinking I was cutting out part of the common ground pathways for the idiot lights and fuel gauge I actually cut out the POWER! Luckily I'd insulated the cut parts just in case so no sparks or blown fuses. I spliced in a pathway on the printed circuit and everythings working fine.
Thanks
John

[MonzaRacer]

Actually for your info the guages have regulated power in the 5 to 7 volt range and bypassing it will burn things up.
The guage has limited power/amps running through it and the sender has a variable resistor in it that changes the current flow through the guage making the needle move.

[NOT A TA]

I just jumped it over the section that I had to cut out to make room for the tach so it should have the same power feeding it. Thanks for the tip though I'll remember that