So after not driving for a while (garage kept for a year), I sent it to a mechanic to fix a crazy-engine-dying gremlin, which I believe is now fixed. Upon receipt, he said, "the gauges don't work". I'm looking to sell it before year end, so I want to get them working.
After reading on these forums through a number of threads and thinking because they were all failing, it was likely the voltage limiter that was the problem. So I bought an IVR3 Voltage Limiter from Real Time Engineering as a replacement. Installed it and still nothing working, but they also included a sensor resister. Using the resister, I could connect each individual gauge to ground through the sensor resister instead of to the sensor. In this configuration, it will set the gauges to read at "full scale".
After testing all 3, they all read full scale. My initial thought was that it was odd that each individual sensor would be out, all within the course of one year. I did cursory checks on the bulkhead disconnect and the 2x4 insulators/disconnects later down the engine harness and there were no obvious issues.
Am I missing something? Is there another single point of failure that would affect all 3 gauges or do I need to start buying sensors?