Voltage Gauge

[Custom06]

We recently replaced the worn out 305 on my son's 86 SWB and after replacing it with a freshly rebuilt 350 our voltage gauge stopped working. We've checked all connections, grounds and still nothing. I don't see any loose connections or grounds anywhere. What are we missing or did the gauge just die. Before we did the swap my oil pressure gauge took a dump and need to be replaced. I thought it was the pressure switch but after replacing it, still not working. Any help would be appreciated.

[ray_mcavoy]

You can test the truck's voltmeter with a multimeter set to measure resistance (Ohms).

Here is a photo showing the back of a typical voltmeter that's used in these trucks:


Measuring between the studs marked "B" and "C" should give a reading somewhere around 122Ω. If you get an infinite (open circuit) reading, the meter assembly is bad (wire coil inside is likely broken) and you will need a new voltmeter.

But if that checks out okay, measure between the studs marked "A" and "C". That should read somewhere around 127Ω. An open circuit reading here could be due to a bad resistor (that's the rectangular ceramic block with blue paint on it), or a bad connection between the resistor and the 2 nuts that secure it to the back of the voltmeter. Loosening and re-tightening the nuts might re-establish the connection if that is the case (just don't over-tighten them). If not, you could replace just the resistor.