[mattfranklin]

Aussie nailed it.

One more grounding issue that bit me once in my '84 S10 was a bad ground to the dash. Erratic gauges and flickering gauge lights. Luckily it was an easy fix and I was super lucky because I accidentally bumped the wire with my leg and that forced the problem to be repeatable with the wiggling of the wire. It was a small ground strap that attached at the left-hand side bottom of the dash, right by the little bracket that attached it to the left kick panel. The vehicle was only about a year old at the time when I started noticing it, so probably loose from the factory. I only mention this because it's one more possible ground.