Need some electrical system help

[oldiesel]

My new to me 91 300D 2.5 which i have only driven about 200 miles since buying it has a strange new electrical problem.First it seems be to borderline for alternator out put with an alternator of only 70amp rating. (My 98 Jetta came with a 120amp) Today it developed a new trick if i rev the engine to about 1500rpm most of the warning lights along the bottom of the instrument panel and the low fuel light light up.Rev the engine a bit higher they go out and at about 2400 they begin to flash on again.Because of the borderline alternator output i have a digital voltmeter plugged into the lighter outlet and the voltage seems to act pretty much normal at these speeds with the exception of going a bit too high if no a/c is on.Anybody have any helpful suggestions beyond pulling the panel and check for loose connections and grounds.Any help will be appreciated. TIA Don

[carnut]

Worn brushes in the alternator.

[oldiesel]

new week bump. I hoped someone would have an easy answer!

[funola]

"if i rev the engine to about 1500rpm most of the warning lights along the bottom of the instrument panel and the low fuel light light up.Rev the engine a bit higher they go out and at about 2400 they begin to flash on again."

This sounds like a ground problem. Check and tighten the engine to chassis ground strap bolts and see if that helps.

[ohiomike]

Your voltage regulator located on the back of the alternator needs replaced.

[sixto]

Answers don't get any easier than carnut and ohiomike provided.

The voltage regulator is a device held on the back of the alternator by 2 Philips screws. Disconnect the battery, remove the 2 screws, extract the device. Most likely you'll find that one or both of the brushes doesn't have a shiny contact area. That means the spring is worn or the brush isn't long enough to make proper contact with whatever that thing is that rotates inside the alternator. At that point you're halfway to replacing it. Some folks have found replacement brushes. Most get a new regulator.

Caveat - maybe your 93 has a newer style alternator with a plastic cover over the back end. I'm not sure how to deal with the regulator on that syle of alternator but it's not too diffierent. I have one in the garage if you need me to check.

Sixto
87 300D

[tobybul]

Might help to know the mileage of this car.... I have not personally used it but Autozone has a free battery/alternator tester service if you bring your car to their store. This might shed some light.