94 C1500 alternator issues
 

Hello! I have a 94 5.7L TBI Silverado that has a fluctuating voltage reading in the dash. Some days, I'll get 14v, other times I'll get 9-10V. It is very inconsistent. This morning it started at 9.5V. I drove the car down the road, cut if off and got 14v. Then I started it again and got 9.5V again. I took the alternator to AZ and it tested good. When I got back and put it on, same low voltage. However, I did notice that the back screw where the single wire (not the harness) bolted down would not tighten up, like it was stripped out. Could this cause my fluctuation? Thanks!

Definitely. A loose connection would do that. You can test the circuit with a multimeter. With the engine running touch the battery terminals with the meter's probes and check the reading. If it is also low then you have to repair the alternator. If the multimeter reads high and the gauge reads low then the gauge is bad. You should repair the loose connection anyway.

a few days late but also check for any loose grounds. They can cause a world of problems.