intermittent alt. failure

ok 96 odbII system. dual batteries hooked together[no isolater]. my problem is that upon start up the alt. or gen. is not working. the gage reads 12 vlts then slowly drops to about 10 vlts. when it gets that low the alt. will start to work. the gage will go up and all of my acc. will work better. was gonna replace the alt. but then read that it is a ext. regulated piece. what should i do at this piont???? ive search on here for simiular problems[ 20 to 30 pages worth but coulndt find anything that helps. thanks for helpin me out.

The engine computer controls whether the alternator is charging or not. Have the dealer hookup the diagnostic computer and verify that the computer is reading the battery voltage correctly.

ok i was cleaning all connections and so forth,and got mad. i took a hammer and hit the alt. and it started to work. i also noticed a little black box thingy that bolts to the back of the alt. 2 connections and a ground. what is that????

tbear said:

...and got mad. i took a hammer and hit the alt. and it started to work...

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While one of my favorite troubleshooting methods - with a surprising success rate - you should probably avoid the hammer when working with any kind of electrical problems.

Yea, it happens, we had an intermittant alt on one of our 97TJ's last month, Replaced it with a new one.

so im not just crazy. was beginning to think i was the only one this happened to. im gonna get one from a dodge i believe it has 136 amps that will help with winch lights stereo and so on.

tbear said:

ok i was cleaning all connections and so forth,and got mad. i took a hammer and hit the alt. and it started to work. i also noticed a little black box thingy that bolts to the back of the alt. 2 connections and a ground. what is that????

Click to expand...

That would be the wires for +12v to the field coil and the wire to the computer (which grounds it to energize the field and charge the battery).