Topic: Charging problem

[snowrun]

I have a 92 Truck, The charge and brake light were coming on weakly and intermittently so I changed out the alternator with one I had laying around that was good when I pulled it. Now, when I hit higher RPMs the lights come on strong and I get a voltage spike, as in the heater fan sounds like it's on steroids. Any ideas? It doesn't seem like I could have 2 bad alts but stranger things have happened.
Thanks

[Gewehr43]

Have you checked your terminals?  How about your battery ground?  My truck had the same problem.  Replaced those and that solved it.

[snowrun [OP]]

New battery, all connectins good, just replaced head gasket & I'm sure the block ground wire is on OK.

[Gewehr43]

I would think the alternator is going then.  Have a local rebuild shop?  I had mine rebuilt for like $50

[kneedownnate]

If you're sure you're getting spikes with higher rpm then the internal voltage regulator may be bad.  Take them both to autozone or kragen, have them test the alts.  Just don't buy your new alternator from either!  Toyota sells factory remans packed with toyota parts.

[Blingn]

at high rpms the belt could be slipn on the pulley.  Is there any rubber resedue on the face of the alternator?  But most likely the alternator is going out due like kneedownnate said and take it in to have it tested they can test it on the vehicle as well as off the vehicle.  With it off atleast you can know one way or the other, but with the whole charging system checked at like kragen or autozone it could be regulator, battery, or a multitude of things