[street rodder 1937]

Hey Guys Can you test a sending unit? My gas gauge is new along with the whole car."a street rod" My gas gauge shoots past full when i power it up.I checked all gounds,One from the gauge to the tank and one from the gauge to the frame.Does the tank have to be full once to get a proper reading.I dont much about ohms. Thanks Randy

[MI2600]

Not sure what kind of car you have. I know on a Chevy, if you disconnect the tank unit the gauge goes to full. When it's connected but you have a bad ground, it will show empty.

It may sound silly, but could you have the gauge connected in reverse?

[street rodder 1937]

Its a chevy.Do you mean discinnect the ground at the tank or the power feed to the tank. Also the ground wire. One goes from the back of the gauge to the tank and the other ground goes to a frame ground from the gauge. Is that right? Randy

[willowbilly3]

Unhook the guage wire from the sender and it should go to empty. Ground it to the frame and it should go to the full reading. If it does this then the guage and wiring are ok and your problem is at the sender. It is possible that you crossed the wires. Basically the sender is a variable resistance to ground.

[5window]

Another thing to consider might be that you have the wrong sender for your gas gauge. Sending units are rated in ohms (resistance) and they vary a lot. For instance, the unit for VDO gauges is 10-180 ohms, while the Autometer,Classic,SW and Dolphin gauges use a 240-33 ohm unit. Note that the former have a higher resistance when full, while the latter have a lower resistance when full. Pre 64 GM's use a 0-30 and post 65's use a 0-90. Check your gauge manufacturer for their specs and then check out your sending unit. Yogi's has quite a selection of sending units. Most are about $25.00