68 Voltage Regulator

[margabuck]

I searched the 170 postings with "voltage regulator" in the title, but no help.

68T 911 with 72T Engine. Complete frame-off restoration with new wiring harness. Used the volt reg that came with the car.

I'm getting 15-16V on the battery during normal driving. Get 13V at low RPM. Assume a faulty voltage regulator...but the Gen light is on all the time, as well. Could be a bad VR or just wired incorrectly.

My VR looks like this...literally a black box. There's a blade terminal at the top. There's a screw terminal at the bottom. That's it for connections. Nothing is labeled.



Wiring diagram looks like this. I fed blue & red wires to the top blade (D+) and the black wire to the bottom screw (DF). Then the brown wire just grounded the entire unit (D-).



My first thought is that the VR isn't even original. Pelican has a VR in stock with the correct terminals so it seems like a no-brainer to just get the Bosch version.

Second thought is to switch the wires. I mean there are only 2 terminals so put black on top and red/blue on bottom. Easy enough. But why have some Oldsmobile GM crap part on my cool Porsche?

Anyone have a 68 that can confirm this VR as OE or is it an aftermarket replacement?

[inaminit]

I have read that the regulator needs to be the same brand as the alternator.
Where is the field DF black wire from the alternator?

[margabuck]

DF blk from alt is the blk wire that terminates at the bottom of VR. D+ red from alt is the red wire that terminates on the top with the blue wire from the large combo gauge (that activates the light that's always on).

[inaminit]

The Bosch alternator harness for a 67-68 terminate in a triple female plug at the vr end, so if your alternator is Bosch, it looks like your vr wires have been changed to use that regulator. I don't know if the motorola are different. There a 4 different alternator harness part numbers for up to 68, 2 each for Bosch or Motorola, and two part numbers for vr's. So it makes sense to go with a vr that is matched to your alternator make and wattage.
Lastly, there was a tiny resistor that Porsche made available in the early 70's to correct for alternator light malfunctions- there may be a tech bulletin on this. I don't know if the part is still available, but if you could get the wattage spec, you could find one that would match.

[expernet]

Same problem here. Ireplaced my regulator on my '69 and it fixed the problem.
The new regulator is cheap, replace it.

[margabuck]

I should have looked here first...quick check of Johnson's Authenticity Guide shows that the Hella VR seems to be standard on the 68 model. What I have is some aftermarket crap replacement that I'm not sure works.

First step is to replace it. I'll circle back.

[margabuck]

RE inaminit: whether to get Bosch or Motorola VR...I've got a '72 engine. Per Johnson, it was random who got Bosch vs Motorola alternators during that year. Since I don't have orig VR, I really need to open up fan housing. I'm going with the Bosch part since it's a 50/50 guess. Seems Motorola part is much less avail and more expensive. Maybe that means Bosch was more prevalent?

[inaminit]

I just worked past some similar problems connecting a 14 pin harness engine into a 67.
If you have access to an endoscope, take off the rh side shroud blocking plate and you can point the snout of the scope inside the air guide and see the face of the alternator.

[margabuck]

Ok, circling back here for anyone's future reference:

The Volt Reg that was installed in my car was this doozy from the 60's Pontiac/Dodge vehicles. Not a stock Porsche part.



So I just took the alt out...it's not that difficult.



And it's a Motorola. I got it cleaned up by a local starter/alternator shop in town for $85. He replaced the bearings, cleaned the brushes, and painted it.





Reinstalled the alt. Also, there was a ground strap between the alt body and the engine that was not connected. It was on the alt side, but not the engine side. So I reattached.

I purchased & installed the replacement Motorola VR.



No more Gen light and the batt voltage stays at 13V while driving.

[mysocal911]

Originally Posted by margabuck

Ok, circling back here for anyone's future reference:

The Volt Reg that was installed in my car was this doozy from the 60's Pontiac/Dodge vehicles. Not a stock Porsche part.


So I just took the alt out...it's not that difficult.


And it's a Motorola. I got it cleaned up by a local starter/alternator shop in town for $85. He replaced the bearings, cleaned the brushes, and painted it.



Reinstalled the alt. Also, there was a ground strap between the alt body and the engine that was not connected. It was on the alt side, but not the engine side. So I reattached.

I purchased & installed the replacement Motorola VR.



No more Gen light and the batt voltage stays at 13V while driving.

Until the rest of the wire insulation disintegrates:

[margabuck]

Circling back here:

Installed old alt and it actually didn't work like it should.

Took it out and installed new alt with built-in VR (and the proper resistor). Still didn't work. It would charge only when RPMs got over 4K. Like I really have to rev the engine up.

Took new alt out and sent it back telling supplier they sent me a bad alt. Got a replacement alt and it STILL DIDN'T WORK. Same issue.

Problem was the bulb I had in the Gen light socket in the combo gauge! I had replaced all my bulbs with LED ones...the gauge lights and the Gen light. When you first turn the key on, the Gen bulb lights up and the alt gets 12V+ through that bulb light circuit. It uses that volt to create an electromagnetic field in the alt...when alt starts turning it starts the charging current.

The LED bulb I used had a miniscule wattage...not enough to create this magnetic field. As soon as I changed back to an incandescent bulb, the alt worked EXACTLY like it should.

Moral of the story: don't use low-wattage LED bulbs in your Gen light socket.

[PeteKz]

Sorry to say it, but that has been documented here multiple times.