My father-in-laws got a '99 Cummins 4x4 manual trans. Truck will sometimes start and run fine. If you shut it off though, then it won't start back up. Just clicks. If you get it started again (like push start it), then it runs fine again until the next time it happens.

Additionally, sometimes it will have the "check gauges" light come on. The alt needle will drop way down, and the lights will dim up and down. If you shut it off, then it won't start again. If you let it run, then it will most of the time recover and be fine.

The truck has had a new alternator, starter, ign. switch, and safety switch installed in attempts to solve this issue. It has had one new battery put on.

My thought is that it must be a battery issue, probably in the battery that hasn't been replaced yet. I originally thought alternator, but since it has a new one, i'm stumped.

 

1. ALWAYS REPLACE BATTERIES AS A PAIR
2. The voltage gauge fluctuating sounds like the grid heater cycling....perfectly normal
3. Are there any codes? Even if the MIL light is not on there may be some stored.

 

I'll ask him about codes and advise him to replace both batteries, not just one.