fuel sending unit/gauge

[narfire]

Electrical can be a tough one for me Sooooo.
Trying to get some of the electrical figured out on the 72 in the shop. Too bloody windy and cold to be outside working today.. so first gauge is the fuel. I have about 1/2 tank of gas, ignition on and no signal to the gauge. Direct wired 12V to the pink and red/grey and have power at the gauge/ light is on. Have an extra sending unit on the shelf and plugged that in. Same thing at the gauge, nothing.
Is there a way to test the sending unit. What settings should the multi meter be set on to see if the current/resistance? fluctuates when the float is moved up and down?
I could go to the parts car and pull the sending unit from that I suppose and check but wanted to stay inside and warm.
Any electrical guru's give some advice?
Thanks
Chris

[RRoller123]

it is a variable resistor, so it should show smooth resistance reading changes as the arm is moved up and down.

[narfire]

Ok, I'll see if I can figure the resistance setting on the meter and see what transpires...

[narfire]

Tried 4 sending units. They all can't be pooched(one from a known working gauge in another 72) but I cannot get the meter to show a change in readings.
Onto some other issue for now I guess.

[azruss]

The sending unit has 2 terminals. one is for the variable resistor and connects to the needle. The other activates the low fuel light. the unit grounds on the gas tank. set your meter on ohms (resistance: will be marked with the greek letter omega: looks like a horse shoe). Connect your meter ground to the bolt flange and the + side to each connector. Connected to the variable side and the ohms should go up and down with the arm movement. If you have any areas where the resistance number changes drastically then you may have a bad spot in the wire. Move the arm up and down several times and see if the meter reads about the same each time. The light side should read infinite and then switch to a small ohm reading when the arm is moved to a specific location.

[narfire]

That is excactly what I needed...Thanks Russ? I'm on it tomorrow.

[vandor]

FWIW a quick test is to disconnect the wires from the sender and ground one at a time. One should make the light come on, the other should make the needle jump to full (don't leave it there long). If this works then you know that everything other than the sender is ok.

[mgbgtn]

Make sure you have 12 volts going through the gauge first then check at the sending unit for power coming to it.