Hey I have a 7.3 idi and the previous owner put a 3g 8.25” dual v belt alternator on the truck. I’ve notice when I put the blinker or wipers on the volt meter goes wonky. I was wondering if it was enough output or do I need a higher output alternator?

 

a 3G is plenty of alternator for an IDI the newer IDI's used the 3G.

I would suggest you have other electrical issues besides just the Fact that a 3G is installed.

 

What could be causing that?

 

Poor wiring to the dash, the factory used small wires whenever possible.

 

Poor connection at the bulkhead or cluster connector can also cause this. My 89 with the AC and headlights on reads low voltage but the batteries stay plenty hot.