Marchal Alternator Trouble--Wiring or Ground?

[Tennessee911]

I have a 71 911 with a 74 2.7 engine. I have a Marchal alternator with an external voltage regulator. Had the car 10+ years but only driven it locally until last month with a 400 mile trip .

My system is not charging. The light has always glowed at idle but went out when the engine was reved up. Battery died on the trip. Bought a new battery, had a digital volt meter and no charge output at the battery. Drove home on new battery and recharged old battery.

When we got home, I removed the alternator and had it tested. Best shop in the area. He said everything tested good--brushes and all, but whoever rebuilt it had paint that kept the alternator from charging and it was now good to go.

Installed alternator duplicating wiring I found. Warning light comes on with ignition and glows all the time. Installed new voltage regulator from host. Still glows.

Took off alternator. Here is the wiring. I could not find another example of a Marchal alternator in the old threads:



1 is a black wire.
2 I think says D- although the - is small. That is a brown wire.
3 is B+ which is 2 red wires.
4 is +61 under the white tape and is a green wire
5 Has nothing connected to it. Is that correct?

I have a big green wire from the main harness and a black wire that
grounds at the left side panel that both ground to the alternator pulley
shroud.

Does the wiring look correct?



The fan shroud is painted black. The edge where the alternator mates with
the fan frame is not completely clean. I removed the alternator from the frame. Could there be enough paint to keep the alternator from grounding?

Not interested in spending money on a new alternator as I am thinking about selling the car.

Thanks for the help.


the alternator from grounding

[timmy2]

Wiring is correct as you have listed it.
1. Black
2. Brown
3. Reds
4. Blue (Fades to green)
5. Big ground wire from top of engine case on one of the case bolt nuts .
Use a number 10 brown wire if you don't want to order a new strap.
Probably the main reason you have a poor ground.

[clarkd]

In reference to your numbering:

I believe #5 is insulated from the alt housing because it connects to the same rectifier plate as #4 where the blue wire connects. I think if you want to add an additional ground wire you should connect directly to the alt housing. (D-)

[Targalid]

I had charging problems with the same alternator set up. Check the blue wire, all the way to the dash light. It provides the current for the exciter. The blue wire goes from the alternator, through the 14 pin connector, through the noise suppressor and voltage regulator, next to the CDI box, and then to the dash. I had a poor connection at the voltage regulator/noise suppressor combination. Check here for a bad connection. Have an assistant watch the alternator light on the dash, with the key switched on, but motor not running, while you jiggle the wires in the blue wire pathway area. When I did this, the alternator light would flicker, cluing me to the ultimate poor connection.

[Tennessee911]

Thanks for the help so far. I have already removed the 2 noise supressors. There are 2 different ground wires now going to the housing so that didn't correct the problem. The blue wire has a new wire end to the spade connector of the new VR.

Going to clean the alt where it connects to the housing and also that surface shown in the housing photo to promote better grounding. Also take this opportunity to clean the red paint off the fan and try to polish it.

Ready to try moving the engine case ground wire from the housing to connection number 5 unless someone is assured that is incorrect.

[E Sully]

Here is a picture of my alternators original wiring.



1 is the Black DF to the regulator. 2 is the brown ground wires to the regulator and micro switch. I don't think a ground strap to the engine was used till they switched to an internal regulator. 3 is the Reds to the starter and rear fuse panel. 4 is the Blue D+/61 to the regulator and then the indicator light. 5 is an insulated connection that should not be used.
The alternator light glowing would show that the wiring to the gage is correct.
Here is my rear panel.

The 2 Blue wires first go to the lower capacitor and then to regulator D+/61, the Black wire first goes to the upper capacitor and then the regulator DF. The Brown wires connect to the mounting screw for the regulator. Since you removed the capacitors then your wires would go directly to the terminals.

[Tennessee911]

Thanks Ed--original photo is hard to beat. Guess Cleaning the joint between housing and alternator is my best chance to fix.

[Tennessee911]

Just wanted to eliminate wiring issues to avoid taking it off again.

[timmy2]

Love this forum, learned something new today about the early alternators.
If I had it in my hands, I would have tested the terminals.
Didn't look like an insulator on terminal 5, just a rusty washer...
Running a ground wire to the case from terminal 2 would help to ground the alternator (instead of or in addition to cleaning the housing)..

[Tennessee911]

Dennis. Good idea about running straight to 2. Will do that but I already cleaned the housing too so couldn't hurt.

5 does have a fiber washer--not a rusty washer. I cleaned with a dremel all the posts and faces of the nuts. Stripping the red fan now.

[Tennessee911]

I ran my brown wire to the bottom sigle spade of th VR. Does that wire also need to be grounded to car body since it was originally fastened to a mounting screw on the wiring panel?

[timmy2]

All I can say is if it is brown, it is ground and if you don't see a direct path or can meter one out, then by all means run it to ground as well.

[Tennessee911]

Ran the ground from the case directly to D-, installed it all back and still have the warning light on all the time. Kind of stumped unless the new VR is bad.

[DohertyCM]

This diagram is from my 74 911....I had the same problems with SEV alternator.
A lot of the time it was the alternator diode going bad...then it would cause the regulator going bad...

It is really really really (did I stress that enough?) important to make sure that the grounding points are clean and have a good connection.
From the battery to the grounding point...
Transmission to the grounding point...
Engine to alternator grounding...

if this is off then it will cause problems.

When the alternators were repaired at the shop...the diodes were always the culprit...
I also had a series of bad or mismatched regulators.....

you are not the only 74 guy who has had problems...I always had a spare alternator and regulator on hand.

[Tennessee911]

Thanks Doherty. I keep thinking my VR is not grounded. I had this one in the car when I started



Based on the Pelican parts list for my alternator I bought this one



The ground from the alternator is on the bottom single spade. Do I need to add another wire to the connector that goes to the single spade and run that to ground? I don't think the VR is grounded as in your diagram.

Here is a photo of the fan that was painted red now polished



Again, thanks for the help!

[DohertyCM]

You need a diagram showing which of the regulator blades are which...so you don't mix them up. I had a hard time finding that...They sell you the regulator but don't mark the points or give you wiring diagram..ARGH! I went through about 4 different types of regulators...2 metal and 2 different plastic case ones... I don't remember the exact points for each. I know I did get one with only 3 points...not 4...that threw me for a loop. I will see if I have a picture showing mine...

Those are things that my Porsche mechanic would say "well you just had to grow up on the Porsche assembly line to know those things".

[timmy2]

Based on the picture of the plastic VR, the single spade is brown (D-) (ground) the spade to the left is Black (DF) and the spade to the right is Blue (D+)

[Tennessee911]

I have had the black on D- and the brown on DF and then reversed them as pictured above. Neither way gets the alt warning lite to quit glowing.

[DohertyCM]

turn the car on and put a multimeter on the battery...what does it read...?

[DohertyCM]

have you considered doing an upgrade and putting a alternator with an internal regulator? a lot of people have done this and removed the external regulator all together...which really is more reliable.?