Bad Alternator, voltage regulator or what? (I know, common theme)

[Jay Laifman]

I have read various posts on this board about alternators and regulators going bad. This is on my '73 with Marchal alternator and VR.

The alternator was rebuilt within the last couple of years by AGS in Santa Barbara. I thought they seemed like old school knowledgable guys. Don't know if anyone has had bad experiences with them. But, they did tell me they could not rebuild my 912 generator, and could have just taken my money.

My car was working fine yesterday. Today, on the way to work, the charging light started going on and of all things the oil pressure gauge started reading really high. Because the alternator was recently rebuilt, and I never replaced the VR, I actually found a new VR near my office at Otto's of Venice. I installed it. Nothing changed. I drove home. I assumed I was running on battery or boiling them, one or the other.

I got home, pulled my multimeter and found that I was getting 12.02 V, with our without revving the engine. At least I wasn't boiling the batteries.

The oil pressure gauge continued to show very high pressure (like 120-140 psi), and it ran poorly, not wanting to idle. I'm assuming that is now because my Warm Up Regulator (on a CIS car) was having issues with the low power).

So, here's the question. Since I changed VR, it seems to be the alternator. Or, will AGS say the VR went bad and it damaged the alternator? Is there any way to know that?

Also, this VR is by HUCO, which I've seen some people say is junk. Could I have got a second bad VR?

[Jay Laifman]

Perhaps I should add this question: how do I bypass the VR and test if the alternator is charging above 12V?

I understand this could be risky if the rpm gets too high. But, I don't know the details on how to do it on a 911.

Thanks.

[304065]

12.0v is a no-charge state from the alternator, the set-point is around 14V
also 12.0v is about a 25% state of charge of the battery.

Charge the battery overnight until you see around 12.5V, then test the voltage a) at the battery with engine at idle and b) at battery with engine at 3000 RPM.

Chances are you have a dead VR which is not charging. Huco aren't necessarily junk, but I don't know what their set-point is, assume around 14V. If you replace with a Bosch solid state it should work fine despite the admonition of the factory to always use the same make of alternator and regulator!

[304065]

Also don't monkey around with the full field test, too much risk.

[Jay Laifman]

Well, I now have a Bosch VR. But from what I can tell, they wire a little differently. The DF wire goes through a small metallic canister immediately before going to the VR. I do not see this canister in the wiring diagram: http://www.pelicanparts.com/911/911_..._CIS_Part2.jpg

Do I leave that canister on, or off, for this? Does a Bosch alt/Bosch VR use it?

[Jay Laifman]

The wiring marking are also confusing. This is actually the Hella version of the Bosch VR.

On the back of the VR it says
D+ DF
D-

And the tabs are on the flip side. So do you read that as if you are looking at the tabs, or as if you are looking THROUGH the VR?

[edmayo]

The canister is a condenser (capacitor) not shown on diagrams but put there to counteract radio interference. Don't need to use it if no new static is heard on the radio. Don't try to out think the markings, take them literally! As you're looking at them. A blue (or maybe red) goes to D+61 (that is for the idiot light circuit) DF should be a brown wire (brown is always ground) And black will be DF.

[304065]

The canister is a condenser (capacitor) not shown on diagrams but put there to counteract radio interference. Don't need to use it if no new static is heard on the radio. Don't try to out think the markings, take them literally! As you're looking at them. A blue (or maybe red) goes to D+61 (that is for the idiot light circuit) DF should be a brown wire (brown is always ground) And black will be DF.

Dear Sir,

One small correction (you mentioned Dynamo Field twice above:

Three connections on a Bosch VR--

D+/61 blue wire
DF black wire "dynamo field"
D- brown wire (ground) and as you say correctly brown is always ground.

Jay, if you want to post a photo before you light it up I'd be happy to take a look.

[Jay Laifman]

Thanks guys. I think I'm good. But, just to be clear, my confusion is not which wire goes to which D. My confusion is which tab is which. Here is a picture of the VR, front and back. I believe that no matter which side I am looking at, D+ is the top left and DF is the top right. However, I was starting to wonder if the picture side was meant to be sort of a see through label - meaning that when I flip over the VR, the D+ becomes the top right. But that's not how any relay or other item I've used before is drawn. So, I think I was just confusing myself.

That said, I have put my car on a battery charger - after driving it home for an hour when this started, so basically running on the battery. And it is charging odd. The charger doesn't say the battery is bad, but when I have it on 6A it is reading 6.3A and when I have it on 10A it is reading 10.7A. And it is not going down. It's only been an hour, but usually I would have seen some motion by now. I'll give it more time and see what happens.

These are pretty new batteries - like no more than 2 years.

[Jay Laifman]

Well, the batteries charged. The car started. But the red charging light would not go out. So it was a nice test.

Tomorrow the alternator comes out and gets shipped to the shop.