The gauges on these trucks are of an old style, and are frequently a problem. Here are some troubleshooting steps to determine where the problem is:
- ICVR: Do any of the three gauges work? If so, it isn't the ICVR - go to Step 2. If none of the gauges work it may be the ICVR as there is no fuse to blow. To test the ICVR put a test light on any of the wires to the sending units and you should see the light pulse. This indicates that the ICVR is working, and the problem is probably with the gauges, the wiring, or the sending units. If the light pulses then go to Step 2. If it doesn't work you need to pull the instrument panel apart to get to the ICVR, at which point you put your test light on the input to determine that it is getting power, and on the output to see if it is working. If it has power and is working you have wiring problems between the gauge and the sending unit. If it has power and isn't working then replace it. But I would suggest building a solid-state replacement as shown here.
- Test Gauge: Pull the wire off of the sending unit for the gauge that isn't working, and ground that wire. Then get in the cab and turn the key to On. The gauge in question should swing to full scale, which proves that the gauge and wiring is good, and that just leaves the sending unit so it must be bad. Or, another way to test the oil pressure or water temp gauge is to swap the wires between those sending units. This may take a jumper on some engines, but that will show you whether or not those two sending units and gauges are working.