I put in a brand new alternator 15 months ago and a few weeks ago I noticed intermittent brake+battery light indicating charging system malfunction. I figured it was a ground because I more recently added a bunch of ground wires due to a hard-starting issue and it went away when I jiggled the nearest grounding bracket.

Today I went to look at it more closely and noticed a big hole in the rubber boot over the positive alternator terminal and a ton of white powder under it. It looks like the plastic insulator broke, causing a short which must have caused a spark. When removing the nut holding the positive cable down I discovered it fused itself to the terminal and broke off when I was removing it (wondered why it was so tight...) and the insulator fell off in a couple of pieces.

It has been a few weeks since the charging system lights and battery is at 12.5v, I'm getting 14.5v at the battery, but 16v at the alternator positive terminal. I'm not sure if I should let me mechanic see if he can safely replace the insulator/nut assembly and keep the alternator or replace it (since I'm not sure if 16v is way out of spec, meaning the voltage regulator is bad, or expected for a nearly-new unit).

 

Your alt is outputting 16 Volts in order to supply 14 at the battery terminal. This is due to the condition of your insulator and connection. you have an intermittent short at the terminal causing heat, heat burns your wire and terminal, and causes resistance.
Return the alternator for a refund, get a different one, and replace the wire.

 

Thanks - the alternator is past the 1yr warranty so no refund. Sounds like from what you're saying that it's possible it's operating correctly but the resistance in the positive terminal connection is what 's causing it to put out more voltage? If so then should I try just replacing the insulator/positive battery cable assembly work first? Haven't been able to find the part # for just that connection.

Is there a way to test the voltage regulator without pulling the alternator?

 

Hard telling what the insulator half on the inside looks like, our alternators dont come apart easily. I believe you have to desolder the stator from the rectifier bridge before you can diassemble the entire unit. TBH I would just replace the whole unit.
No regulator test necessary, it puts 14V into the battery or it doesn't. The battery is getting 14.5, so the regulator is good.
That short was not good for the alt, if its not already damaged, then its certainly been compramised.

 

The ALT generates ALOT of current for the car. In fact, all of the current. A faulty one, as this one already has shown itself to be, would increase the risk of a major electrical issue, like an electrical fire, should you choose to repair it.

I would eat the cost and replace it for peace of mind.

 

Thanks for everyone's input - new alternator is on the way. I like how I went with a brand new one to avoid having to replace it again and it craps out 3 months after warranty is up.

 

Which is a good argument for buying reman. They both can be built with crappy components, so why get the more expensive one?

 

Check that charging wire out real good. You can bypass it with 10 gauge fused wire if need be. Solder all connections.

 

The brand new was $140 this time ($122 the first time) on Amazon. The remans were abot $130. In theory the new should be less of a crap-shoot, and I'm not limited to the same brand of reman for replacement.

 

New Nissan, or New aftermarket? The reman is usually a gutted Nissan.
I would tend to think that;

New Nissan>Remanned Nissan>Aftermarket new.

 

It's a Bosch. The problem w/ the reman process as I understand it is they only replace the most worn aspect of the alternator that caused the immediate failure, and our originals last so long (mine went out at 190k miles) I figured that any reman is going to have some parts that wear that are still original and on their last legs.