Alternator won't charge

[BDD]

When I turn key to 'on' ammeter idiot light comes on. and ammeter reads a slightly negative current, meaning current is coming from battery.
When car is started light stays on and ammeter continues to read negative. When engine is revved, ammeter light dims and ammeter needle moves to read slightly less negative.
Voltage regulator is new.
Battery posts and terminals are cleaned and tightened.
The brass nuts on the 4 main lugs in the fuse block are tight. I cleaned them a few years ago but have not recently.
When running, engine dies immediately when positive cable is removed from battery.
When I measure voltage at regulator with engine idling I get a very low reading, maybe 2.5 volts.
I would say that the alternator is not working but I suppose that there could also be bad or loose wiring that is causng it to not charge.
Recently I measured 14.5 volts at the reguator and the ammeter showed a positive charge but that was brief and it went back to a negative charge. That this happened briefly could indicate an issue with wiring rather than a bad alternator?

Suggestions?

[namba209]

If you have the original style regulator, it could be nothing more than pitted contacts inside the can. They can be sanded smooth, carefully, and put back in service. If it's an after market "solid state" regulator, then probably the alternator has gone south. For checking operating voltage, I usually go straight to the battery posts, checking prior to engine running and during engine running, but the same check can be performed at the 4 studs in the fuse panel with the positive (red lead) of the VOM and a good ground with the negative (Black) lead. HTH.

[tekenaar]

Originally Posted by namba209 If you have the original style regulator, it could be nothing more than pitted contacts inside the can. They can be sanded smooth, carefully, and put back in service. If it's an after market "solid state" regulator, then probably the alternator has gone south. For checking operating voltage, I usually go straight to the battery posts, checking prior to engine running and during engine running, but the same check can be performed at the 4 studs in the fuse panel with the positive (red lead) of the VOM and a good ground with the negative (Black) lead. HTH.

. . . in addition, check the 3-wire lead between the alternator and regulator for good contact, paying specific attention to the blue/white "idiot light" lead. If that lead does not have good contact at the alt/reg, the alternator WILL NOT CHARGE!

. . . also, is the alternator spring clip plug retainer in place on the wire plug coming from the regulator?

[opelbits]

I would suspect the alternator. Pull it out and have an auto electric shop test it. Autozone and such can do it, too, but they can be idiots at times.

Check your belt too, it may be slipping.

[BDD]

The regulator is brand new and a solid state one. I replaced that recently, the alternator indicated a charge which it didn't before (so I thought t was fixed) then it stopped working so I bought a second regulator. The regulator itself should not be the problem.

Looking at the manual wiring schematic I may have switched the black and red/blue wire sides briefly. That may have caused the problem.

I tightened the fan belt yesterday and that made no change.

I've removed and cleaned the grounding from alternator and battery to ground on the engine block with no change. I also used Scotch-Brite where the terminals meet the engine and alternator so that should be good. I also measured resistance in the cable from alternator to engine and battery negative post to engine and got very low resistances in the cables themselves. I have not done the other side. The connection of the grounding side to engine is covered in grease.

The wire retainer clip is on the alternator and the screw heads look rusted.

I was going to remove the wiring harness from alternator and regulator to make sure all connections are still good. The wiring and fuse for that are new. One of the first things I corrected from the previous owner.

The ammeter idiot light comes on does that mean the blue/white wire is properly connected between alternator, regulator and ammeter?

Today after cleaning the grounding the idiot light seemed less bright but the ammeter needle was just as negative. That could just be because I was viewing it in the dark last night and it's very bright out now.

Thanks for the replies. I think this helps anyone who's trouble shooting what could be causng their battery to not take a charge.

Any more thoughts based on this? I don't want to replace the alternator if that's not the problem.

[namba209]

Yes, if the Blue/White wire is connected correctly the lite will come on with the key on and the engine not running. With the engine running and the alternator putting out system voltage, the lite goes off, because there will be system voltage on both sides of the lite. Best bet is to take the alternator to an auto parts store that has the capability of checking it out.

[BDD]

Yeah, I'm thinking it's probably the alternator based on the above. I think I might have a spare one in the garage.

I took the wiring harness that goes between the alternator and voltage regulator off tonight to check it. Measuring every wire from end terminal to end terminal (to make sure they were connected to the wires properly, and thta the wires were good, etc.) I got 0 Ohms. So that must not be the problem.