[Ramblin Fever]

FWIW - just because your volt gauge is normal does NOT mean the alternator is 100% efficient.

My volt gauge read on the + side even when I had a dead alternator; I drove home 300 miles one night on a dead alternator, obviously I never shut the truck back off, and I had very limited use of electricals - i.e. truck literally shut everything down except one headlight, I didn't even have dash lights for the last 150 miles in. Driver's window was stuck in the down mode on that rather cold night with obviously no heat, not enough power to put it out.

Long story short, it fried the battery along with it, but I made it home. It was 10pm the night it failed up on the flat-tops in the Colorado mountains, an area with no open part stores, and definitely no availability for an Isuzu alternator.

Don't rely on your volt gauge, go somewhere where they can test that alternator under a load - I can almost guarantee you if it's the original it's probably shot!

I have a '97 Rodeo, and my OEM alternator crapped out at 50k miles (covered just barely under warranty); my 2nd alternator failed at 130k-ish miles. So it would not be a surprise to hear yours is getting old.

If you do end up replacing it, go with either an OEM or a Bosch unit, do NOT use just any aftermarket alternator or you'll be experiencing issues in another 3-4 months.