I have a 95 2WD 5sp that I had a reputable trailer dealership install a 7 way RV wiring connection for a new trailer I just purchased. After the intallation and before towing the trailer I noticed the battery light on and the gauge showing 10-11. The tach was also going haywire. After stopping and not finding any loose connections under the hood or with the new wiring job the light and gauge went back to normal and the tach calmed down. I drove on and could hear a slight whining from under the hood which stopped after a few minutes but the tach would go haywire when I turned on the headlights and would jump around when I used the turn signals. The installers left the key in the on position for about 30 minutes when they were doing the wiring job. Could this have messed up my altenator which is causing the tach to flip out?

While the tech may have drained your battery by leaving the key on, I would be more concerned that the glow plugs continued to cycle for 30 minutes. That can't be good for them.

I'd take the truck home and put it on a small battery charger overnight. Then see if you have any issues. From what you describe, it does sound like the alternator is going back. I've had six alternators in my truck. Some went bad at the bearings, others had electrical issues. They were almost always diagnosed with low voltage or tach problems.

Jake

I've actually had no starting/driving issues. I took it back to the trailer dealer and had everything double checked for possible casues. Both batteries and the altenator showed they were charged/operating properly. They are going to put on a new altenator as a resolution but I was hoping someone could enlighten me as what else a possible cause would be since they are footing the bill.

Loose belt. Worn out stretched to the limit, tensioner maxed out.

Thanks for the input. I'll check that as well.