Fuel Gauge driving me crazy

[mpierce9]

ok, several months ago I had started this thread regarding my fuel sending unit.

Original Fuel Sending Unit conversation

Tunrs out the sending unit works great. The gauge also works great. The brown wire between the sending unit and the fusebox also reads and works great. The problem is that everything only works great with the car powered completely off. I checked with a multi meter. i confirmed the multi meter batteries were brand new.

I've checked the gauge directly to the battery and sending unit and it reads PERFECT. Unless I turn the key to acc, start, or the truck is running. Then everything reads at 100% resistance on a multi meter and 3:00pm on the gauge. This is the part that confuses me. The gauge is laying next to the battery on a piece of wood and is only connected to three different wires at this point: directly to ground on the battery, directly to hot on the battery, and a splice to the sending unit. in this scenario it still goes to 100% resistance when the power is turned on.


I'm not sure where to begin.

• I read 64 OHM resistance on the tank currently (about 3/4 a tank) with the power completely off.
• I read it everywhere on the brown sending unit line, on the gauge and everywhere along the line, with the power completely off.
• I can trick the gauge into any reading I want using resistors.
• I can read the exact fuel level if I power the car off and hook the gauge to the power and ground on the battery and the fuel reading post directly to the sending unit wire

What would cause the entire system to read 100% resistance to ground when the power is turned on to the car but not when it isn't?