Join Date: Sep 2000
Location: Shrewsbury, MA, USA
Something not documented in any of the various wiring diagrams for the console gauges is that you need to add a ground jumper wire between the two metal gauge mounting brackets, since there is only one ground wire in the gauge wiring harness, and it normally lands on the rear bracket. The fuel and temperature gauges need this ground, as do the lights since they ground to the metal bracket.
The fuel gauge is pretty simple, it only has one power terminal, one ground terminal and one connection to the sender. Some of the repro gauges require a 46 ohm resistor to be installed across the power and sender connections (take the one off the back of your old fuel gauage), some have the resistor installed inside the gauge.
The bottom terminal of the gauge is the ground connection. It has a plastic insulator on the stud and sometimes needs an additional ground wire added to the stud to get a good ground.
Check for voltage at the sender connection in the trunk with the key in the run position. If you can measure voltage there, then the guage is getting power (won't necessarily be 12V but will be greater than 0V). Make sure there is no voltage with the key off.
If you have voltage there, then ground the connector to the car body, gauge should indicate empty. With the connector disconnected the gauge should read beyond full.
While the connector is disconnected stick an ohm meter on the connection going to the sender in the fuel tank. You should get a reading between 0 ohms (empty) and 90 ohms (full). If you have half a tank you should see around 45 ohms. If you don't get a reading (infinite resistance)then the problem is between the connector and the sender ground wire. The sender is grounded to a stiffener right in front of the gas tank, there is a black wire coming out from above the tankattached to the underbody frame stiffener with a sheetmetal screw right above the rear axle.
Key needs to be in the run position for the following:
If the gauge reads empty all time then either it is not getting power, has an short circuit (ground) to the sender or has a bad ground at the gauge.
If the gauge reads full all the time, either it has an open circuit to the guage, or it's missing the resistor on the back of the gauge.
If you can manually put the needle in the middle of the guage and then disconnect the sender in the trunk and the guage does not move to the empty position (assuming it has power to the gauge) you are missing the resistor, or gauge ground.
The temperature gauge isalmost the same as the fuel gauge, it only has one power terminal, one connection to the sender, an 86 ohm resistor (91 ohms works better) that connects from the top terminal of the gauge to the bottom (ground). The resistor controls the amount of feedback current which drives the needle downscale. without this reistor once the needle moved upscale to the normal operating temperature position it would stay there forever.
Make sure you didn't use teflon tape, or any other non conductive sealant on the threads of the temperature sender because it will insulate the sender and result in an open circuit.
Also make sure you have a temperature sender installed that works with a guage, not a temperature switch that works with the idiot light.
Check for voltage at the sender connection at the engine block with the key in the run position. If you can measure voltage there, then the guage is getting power (won't necessarily be 12V but will be greater than 0V). Make sure there is no voltage with the key off.
If your getting voltage at the sender end of the wire touch the sender wire to ground, this should make the gauge go to hot. Remove the sender wire and the gauge should return to the cold position.
1969 Indy Pace Car
350/300HP RPO Z11
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