the guage on my 67 camaro goes from 8 o'clock (empty) to 12 o'clock (full) when unplugged the wire in boot guage sits on full mark perfectly tested the sender seems to work fine filled the tank and i got 91 ohms, so would this be a resistor problem? or is the guage niddle in the wrong spot?
how and where is this resistor?
Okay lets just make sure we both know what you found:
Needle sitting past full usually means a bad sender ground at the rear of the tank hanger strap.
so you unplugged the connector in the trunk or "Boot" you get past full.
Next step in the troubleshooter was to ground the gauge side of that lead in the trunk to see if you get past empty. Did you get past empty?
If "yes" then the gauge and wiring to it from the trunk is working.
If "no" then you need to test continuity through the wire to the gauge at the cluster end.
If that checked out then the gauge should be tested as it is suspected as being bad. If the continuity failed on the harness, then you need a new run to the trunk for the gauge or replace the Fisher Body harness.
When you tested the ohms from the sender was it before the tank was full? What was the reading? If not siphon half of the fuel back out to a Gerry Can and test again. You should have 45 ohm's with half a tank. If you still get 90 plus your sender is stuck in the up position.
Dash mounted fuel gauges in 1967 & 1968 used a printed circuit board with no external resistors on the back. But I think there is an adjustment screw or maybe that is for the Tach if equipped.
You can bench test the gauge with a 0 to 100 ohm "potentiometer" which will send a various amount of ohms at the unit to electronically reproduce the senders signal to the gauge. If it is working the gauge should move from empty to full and every where in between as you select a "volume" in the potentiometer.
But the long and the short of it is that if you can get 45 ohms from the sender and get half a tank-ish from the gauge, Then your 90 plus is maybe from getting more then 18 US Gallons in the tank and it really is past full. I would also if I had the cans pump the tank dry and see if I get past empty, then with the gauge on pour in one 5 gallon Gerry Can and see if I had about 1/4 on the gauge.
Hope that helps find the gremlin