Rev to 3k before alternator kicks in

[Diesel Fumes]

Once its kicked in, its fine.  Will work below 3k rpm, but will drop to 0 then shoot back up during a gear change.  Give it some throttle and bring it to 3k and then it works all the time.  I have a replacement alternator, but its a rebuild.  There is a Bosch in the car now.  Could this be a sign of the alternator on its way out?

Also, when its not registering the revs, it will not charge.  Lights brighten when it kicks in etc.

[Vincent Waldon]

Tach is getting its signal from the alternator... so the two are very much related.

Yes, it sounds like an alternator on the way out... first to check would be the brushes since they are a wear item and when worn often present as intermittent charging, usually RPM dependent.

They come as part of the regulator assembly can be removed and inspected with the alternator in place (two screws, disconnect the battery ground first) and a replacement regulator assembly is reasonably inexpensive.

If the brushes are worn it's probably wise to check the commutator for grooving... if the commutator is worn as well you're wasting your money on new brushes... rebuilt time !!!

[burn_your_money]

It could be a loose belt or a poor connection on the alternator. I know when my belt was slipping I was having the exact same symptoms (there was no belt squealing either)

[Vincent Waldon]

It could be a loose belt or a poor connection on the alternator. I know when my belt was slipping I was having the exact same symptoms (there was no belt squealing either)

Even better idea... belts are wear items too !!

[Diesel Fumes]

Gosh.  I went to change the alternator and realized the blue wire had come off.  Now its fine.  Except the battery light stays on until I blip the throttle just a bit.