calling all electrical gurus / Alternator help

[jimtweet]

so its got a couple mechanics stumped and I really need to get to the bottom of this.

The car is a 1979sc

While rebuilding motor and adding AEM / EFI and such I upgraded to the Valeo Internally Regulated Alternator. I purchased this alternator from Pelican, installed, motor sat on stand for roughly 6 months before installing.

Finally the day came to have car towed to tuners. Tuner calls, good news, car fired up, bad news, alternator is not charging battery.

here is where the fun begins...We did a few tests on alternator while it was in car, all concluded the alternator was bad.

I removed the Alternator, took to local alternator shop, he bench tested the alternator in front of me, says "yep its bad, zero output". I tell him to go ahead to order parts and rebuild. Calls me 24 hours later, ready for pick up.

Install "rebuilt" alternator, start car, same ****, not charging.

here is what I have, just to double check my wiring.
1. Large Red wire from positive terminal on alternator to starter
2. ground strap from negative terminal on alternator to top of engine case
3. blue wire running into main engine harness (exciter wire, I believe its called)

here is what we checked
1. voltage at battery is 11.8 (not running)
2. voltage at positive terminal on alternator is 11.8 (not running)
3. continuity of ground strap is good
4. continuity of blue wire from alternator side to gauge idiot light side is good.
5. if we remove the blue exciter wire from alternator, check voltage, 11.8
6. when I turn key to on position, alternator idiot light comes on, so therefore I know the bulb is good ( I read if bulb is bad, this can cause non charging)

questions
1. possible the alternator is still bad?
2. is there any wiring that im missing to alternator? I don't believe so cause there is only 3 freakin studs
3. last question, my fan housing is powdercoated, is the alternator supposed to ground itself through its case to fan housing to engine? In other words. should I run a ground wire from engine block to the back of one of the mounting bolts from alternator to fan housing

[acme911]

3. last question, my fan housing is powdercoated, is the alternator supposed to ground itself through its case to fan housing to engine? In other words. should I run a ground wire from engine block to the back of one of the mounting bolts from alternator to fan housing

Yes! Run a ground wire from block to mounting bolt on alternator.

[acme911]

This Pelican has an alternator for sale and has a pic of the Oem ground strap:

FS: early 911 Fan, Housing and Alternator

[Targalid]

Did you check that the main engine ground from the tranny to the body, next to the shift tunnel, is tight? Is the ground good from battery negative cable to the body?

[jimtweet]

Originally Posted by Targalid

Did you check that the main engine ground from the tranny to the body, next to the shift tunnel, is tight? Is the ground good from battery negative cable to the body?

New ground strap, tight as can be. New ground strap from battery to chassis.

[Walt Fricke]

Remember, the battery started the car, so the problem is most likely not connections to the battery.

I had the voltage regulator pack up on a 3.2 at night, so car stopped when battery drained. Replaced it, and within a month the car went dead in the daytime. Took it to a shop fearing I had messed up. Mechanic said I did install correctly, but the new VR was defective.

Yours would have to be nearly immediately defective. You might ask the repair shop if they test after repairs. They should be able to test the VR they installed (assuming they did) before they send a rebuild out the door, but maybe they don't?

Or does the '79 still have the external voltage regulator? Is that hooked up correctly with D+, D-, and DF, all of which come from studs/posts on the alternator? From your description of only the one blue wire, plus ground and D+ to starter, it sounds like the internal regulators started in '78, as my '77 had the external regulator.

The alternator B+ also has a red wire running to the rear fuse panel for the heater blower, but not hooking that up (usually both that and the wire to the starter -which is how the battery gets charged- is crimped into the same ring connector with the starter wire so you can't mess this up) won't affect battery charging.

[mysocal911]

Or does the '79 still have the external voltage regulator? Is that hooked up correctly with D+, D-, and DF, all of which come from studs/posts on the alternator? From your description of only the one blue wire, plus ground and D+ to starter, it sounds like the internal regulators started in '78, as my '77 had the external regulator.

The first internal regulator used on a 911SC was in 1982. When installing an internal reg alt in an external
reg alt engine, the external alt must be fully disconnected with only the blue wire being used.

[jimtweet]

Originally Posted by mysocal911

The first internal regulator used on a 911SC was in 1982. When installing an internal reg alt in an external
reg alt engine, the external alt must be fully disconnected with only the blue wire being used.

Which I have done

[HaroldMHedge]

Did you use a TSB for the updated alternator?

There are two TSBs issued on the use of an alternator with an internal regulator in earlier cars that I know of.

Installing new alternator w/ internal VR has Technical Bulletin 1 - New Alternator has Integrated Regulator. Several other site threads also have this TSB.

Here is what I think is a later TSB addressing the installation of internal regulated alternator in a little more detail.









This should help with the troubleshooting.

Harold
87 Carrera coupe

[mysocal911]

Next you need to verify that the alt light (blue wire) is not shorted to ground, not providing the
required startup current. This requires removing the alt and disconnecting the blue wire and seeing
if the light goes out. Also, hopefully the blue was connected to the correct post (61). If those check,
then either the alt itself or the reg is bad.

[pete3799]

You do have the external regulator unplugged right?
The black wire in the alt. harness is not used.

[jimtweet]

Originally Posted by mysocal911

Next you need to verify that the alt light (blue wire) is not shorted to ground, not providing the
required startup current. This requires removing the alt and disconnecting the blue wire and seeing
if the light goes out. Also, hopefully the blue was connected to the correct post (61). If those check,
then either the alt itself or the reg is bad.

This was checked. If I remove blue wire from alternator, the dash light goes out.

Yes blue wire is on correct post.

[jimtweet]

Originally Posted by pete3799

You do have the external regulator unplugged right?
The black wire in the alt. harness is not used.

Car has AEM stand alone engine management so the car has been somewhat rewired. So yes, all the external regulator wiring has been removed.