My Ampmeter started to act (swing neg/pos) erratic when I step on the gas. At idle the meter is at zero.

 

If you can re-create the problem, have someone hold a voltmeter on the battery terminals while you rev the motor. If the voltage is jumping up and down, you definitely have a problem. I would not trust the factory meter by itself.

If you have a problem, I would look for any loose or corroded connections. You may want to wiggle the wiring around while watching the voltmeter on the battery, instead of revving the motor. You may find a broken wire in the harness this way. I would un-plug and scrape clean all the connections at the regulator and the alt, and the connection on the starter relay that goes to the battery positive. If none of this helps, you can then start replacing parts. I think the alt would be a first best guess.

 

Thanks. I will try the simple items first. Is there a way to open the alt and inspect the insides for problems?

 

Well, you can open it up and check the brushes and slop in the bearings. I would have some sort of manual with me to help guide in the tear down. Also make sure you take a punch or magic marker and mark all the places it splits apart, so you can get it oriented correctly when you put it back together. There is also a little trick with paper clips to get the brushes re-installed, and the manuals tell you how to it.

 

Found a nut off the ground wire on the alt. There is a small metal control box on the back side of the alt were the wire was coming out of. I drove around after installing a nut a the ammeter woked fine. I also check the voltage at the battery, voltage was steady. Ohm'd the wiring from the alt to the starter relay, checked OK. Will have to drive for a while longer to see if the problem re-occurrs. Thanks for your help! P.S. it's a Motorcraft alternator.

 

That box sounds like one of those regulators that is mounted to the back of the alt. If the regulator did not have a good ground, that could certainly have been the cause your problem.

 

Thanks dave!