Strange red light/alternator issue

[Stevehose]

I drove my coupe for 2 hours today - no issues and runs great. This evening I go to move it in the garage and when I start it the red light comes on but doesn't go off as it usually does. It dims slightly when I rev it but doesn't go all the way off. I let it idle for a while as I adjust my driving lights then turn them off so no high demands on the electricals - still red. I turn the car off with the light still acting up. Later I come back and start the car up and the red light goes out as usual. I have a new Optima battery and new high amp output alternator (occasionally it whines slightly when I put on the high beams/driving lights but sometimes it doesn't. (????). Disconcerting behavior.

The alternator has it's own regulator and I have bypassed the stock one. Any ideas on what to look for or what to test for?

 

[61porsche]

What's your measured output? In other words, is it charging but just the light is the problem.

Check the wire that goes to the light ( exciter) for loose connections, etc.

 

[roundel]

Almost certainly the brush pack is worn out. You can remove it by taking the two screws out.

 

[x_atlas0]

Did you ground the alternator housing? On the older models it wasn't much of an issue, but the newer, internally-regulated ones need to be externally grounded. Check your operational voltage.

 

[Stevehose]

I will look into all the suggestions, since it is a new alternator I hope the brushes aren't bad. Should I ground the alternator directly to the battery terminal or will the frame suffice?

Did you ground the alternator housing? On the older models it wasn't much of an issue, but the newer, internally-regulated ones need to be externally grounded. Check your operational voltage.

 

[x_atlas0]

I will look into all the suggestions, since it is a new alternator I hope the brushes aren't bad. Should I ground the alternator directly to the battery terminal or will the frame suffice?

I grounded it to the engine directly. Also, I went through alternators because the diode pack on the back was bad. This will make the light come on a little even though the voltage is high and the car will not charge. This made things difficult to diagnose without a true testing apparatus, or at least an ammeter.

 

[roundel]

Original alternators don`t have rubber bushes and so don`t need a ground cable. If you fitted one with rubber bushes then it will.

 

[Stevehose]

Results

I fitted a ground wire from the alternator housing to the engine block. I checked all connections to the alternator for tightness. Red light goes out as normal so something worked. Here are my voltages:

At battery engine off: 12.75 volts
Engine idle no accessories: 14.40 volts
Lights on idle - 14 volts
High beams on idle: 13.5 volts
High beams and driving lights on idle (super bright!): 12.75 volts

The volts go up toward 14.40 as idle speed goes up if the lights are on, it stays at 14.40 volts regardless of engine speed with no lights on.

Are these readings normal? Thanks.

 

[x_atlas0]

I fitted a ground wire from the alternator housing to the engine block. I checked all connections to the alternator for tightness. Red light goes out as normal so something worked. Here are my voltages:

At battery engine off: 12.75 volts
Engine idle no accessories: 14.40 volts
Lights on idle - 14 volts
High beams on idle: 13.5 volts
High beams and driving lights on idle (super bright!): 12.75 volts

The volts go up toward 14.40 as idle speed goes up if the lights are on, it stays at 14.40 volts regardless of engine speed with no lights on.

Are these readings normal? Thanks.

That sounds right. You don't want much higher because it will mess up the battery.