good evening all. in my 1987 GTA my temp and oil gauge is not working. i figured since they both stopped working at the same time its not the oil sender or temp sensor on the engine block. my cluster was kinda beat up and plastic was cracked. so i did get a verified working new cluster and the same thing. just looks better. Could both sensors quit at the same time? thanks in advance.

 

Does the tachometer operate? If so, the GAGE fuse power feed to the cluster is probably intact.

If you suspect a sensor or sensor wiring, the green wire to the coolant temperature sensor can be grounded to force the gauge to the full-scale (hot) position. If grounding the wire does not peg the temperature gauge, check the wiring through the C100 connector and to the cluster. Keep in mind that the connectors at the corners of the cluster have been know to create problems in the past.

The oil pressure circuit functions a bit differently in that grounding the tan sensor wire should force the gauge to a 0 pressure indication, and through a 90Ω resistance to ground the gauge should indicate full-scale pressure. That circuit also routes through the C100 connector and to the cluster connectors.

It is also important to verify good grounds at the engine, most commonly at the rear of the right cylinder head/intake area.

 

i believe gauges work, oil goes to 60lbs when turned on and the temp goes to max then back to zero. i will check grounds. my fans are riged to stay on all the time. someone else rigged it up that way. but its been like that for awhile but the temp was working still. ill checks grounds

 

Sounds like the wires are disconnected at the sending units.

In both cases, the "danger" condition (0 oil pressure, and max temp) are indicated by the sending units to the gauges, as a short. In the "happy" condition (max oil pressure, very low temp) the sending units both go to very high resistance, which is more or less equivalent to an open circuit.

The temp gauge has a connection to the ign sw that makes it peg (if it was a light, it would act as a "bulb check" by turning the light on) during Start. The OP gauge does not have this.

Check the wires.

You can verify that the gauge works by shorting them to ground at the sending unit end. Doing so should make the temp gauge peg and the OP gauge go to zero. If they do this, then the gauges and wiring are fine.