Altenator/Voltage issue

I'm chasing a charging circuit problem. When I turn on the master switch, in car and external voltage meters show 12.5 volts. Turn on the ignition, voltage drops to 11 volts. When I start the engine, the voltage remains the same, so the altenator is not charging and the battery is draining.

I have replaced the alternator, and the voltage regulator. I then checked the continuity of the wires from the field terminals on the alternator to the voltage regulator plug. One tested ok after moving the probe aroud a while, but I could not get any continuity on the other wire. So I am replacing the voltage regulator plug. Grounds are all good - brand new cables.

Any tips?

An off-the-wall thought, don't have ANY idea if it correlates to your car. As I recall, on our P-cars, the alternator (warning) light bulb is part of the circuit to excite the alternator field circuit (please be gentle on me if I've got this wrong, I'm just a dumb Mech-E, not a Double-E), and if the bulb is blown out or missing, it won't charge - the alternator never starts putting out. Have you perhaps removed enough of the stock dash to lose this?

Of course, I've seen the other end of the spectrum in the day job... a new engine cal from a certain manufacturer, when downloaded into our prototypes... well, let's just say the dumbasses in Powertrain forgot to include the code/switch to send out the message that would tell the alternator to charge the battery. So suddenly all of our cars started eating batteries, for no good reason. I still don't remember how they figured that one out!!

Some more tips from a bud who used to run an ITE Omni...

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One is to switch to the more durable Bosch alternator, but first I would suggest
he run a ground directly from the alternator to the negative battery terminal.
I did both of these things on the GLH-S race car, and never had a problem since.[/b]

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An off-the-wall thought, don't have ANY idea if it correlates to your car. As I recall, on our P-cars, the alternator (warning) light bulb is part of the circuit to excite the alternator field circuit (please be gentle on me if I've got this wrong, I'm just a dumb Mech-E, not a Double-E), and if the bulb is blown out or missing, it won't charge - the alternator never starts putting out. Have you perhaps removed enough of the stock dash to lose this?

Of course, I've seen the other end of the spectrum in the day job... a new engine cal from a certain manufacturer, when downloaded into our prototypes... well, let's just say the dumbasses in Powertrain forgot to include the code/switch to send out the message that would tell the alternator to charge the battery. So suddenly all of our cars started eating batteries, for no good reason. I still don't remember how they figured that one out!!
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Vaughn: Thanks for the reply. None of the service manuals that I have refer to a warning light in the circuit. I'll double check just to be sure.

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Some more tips from a bud who used to run an ITE Omni...
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Item #2 is easy enough. We'll give that a try, probably right after replacing the voltage regulator plug (new one just picked up from NAPA).

I don't know if this applies, but my alternator has a big pulley on it to slow it down so it doesn't burn up running 6000+ rpms all day. The down side is, it won't charge while under 3000 rpm or so.

Also, I chased a bad wire for 2 years on my car. When I'd hit the wire with a probe from a meter it would flex the wire and would show good connection but when I pulled the probe off, the wire would flex back into a non-connective way.

Good luck.

I just dealt with a similar issue. I think the big clue here is that when you switch on the ignition your voltage drops to 11. You've got a big voltage drop somewhere - check your battery voltage under those conditions and it'll probably be well over 12. On my car the crimp terminals at the alternator and at the master cutoff switch were corroded. Check each connection with a volt meter across the connection while current is flowing - an ohm meter won't show the problem. Check from the alternator + to the battery + and from the alternator case to the battery -. Track down where that voltage drop occurs.



I also had underdrive pulleys on both the crank and the alternator - removed the one on the alternator. With all the fixes now my full load battery voltage is about 1 volt higher than it was.

Fusible Link?

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Fusible Link?
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Manuals show that I have them, tell me where in the circuits they are, but not where they are physically.

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I don't know if this applies, but my alternator has a big pulley on it to slow it down so it doesn't burn up running 6000+ rpms all day. The down side is, it won't charge while under 3000 rpm or so.

Also, I chased a bad wire for 2 years on my car. When I'd hit the wire with a probe from a meter it would flex the wire and would show good connection but when I pulled the probe off, the wire would flex back into a non-connective way.

Good luck.
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Thanks.

Two wires going from field terminals on the alternator to the voltage regulator - one shows good continuity, the other shows no continuity or momentary if I move the probe around enough in the voltage regulator plug.

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I just dealt with a similar issue. I think the big clue here is that when you switch on the ignition your voltage drops to 11. You've got a big voltage drop somewhere - check your battery voltage under those conditions and it'll probably be well over 12. On my car the crimp terminals at the alternator and at the master cutoff switch were corroded. Check each connection with a volt meter across the connection while current is flowing - an ohm meter won't show the problem. Check from the alternator + to the battery + and from the alternator case to the battery -. Track down where that voltage drop occurs.

I also had underdrive pulleys on both the crank and the alternator - removed the one on the alternator. With all the fixes now my full load battery voltage is about 1 volt higher than it was.
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Thanks, Marty. I give the tests a try if the voltage regulator plug does not work.

OK, got the new voltage regulator plug spliced in - good continuity on both leads. I also added the direct ground from the altenator ground to the battery. Fire it up tomorrow and check voltage. I will also look for any voltage drops.

Thanks for the suggestions. Root cause looks like the voltage regulator plug. With kill switch on - 12.5v. Add ignition - 12.5v. Engine on - 14v.

I did add the new ground directly from the altenator ground to the battery.

ITFest, here we come!

Mo' betta, see ya there!