Alternator wizards, this charging problem is killing me!

[Lee]

I have a '78 SC. The alterntor in it is a Parish-Rhone, 60 amp, external regulator. The regulator has been a Marchal...big balck plastic cover.

My generator light comes on, and stays on. Alternator has been checked three times, battery twice. Blue wire has continuity, and maybe a .3 volt drop between the battery and the 11 pin connector. No resistance between the connector and the alternator/regulator. The grounds are good. DF wire has continuity. The red wire is delivering full voltage to the alternator, when the engine is off. Has to be the regulator, right?

I took my old regulator apart, and found a fried resistor and a shorted capacitor.

I replaced the regulator with one from a local parts store...a borg-warner. It worked for a minute, and then quit. Started up again, but went out when I went over some railroad tracks.

Today I replaced it with a mail order specifically for my SC. I turned on the car, the generator light stayed on. Then it began to flicker. Then I heard it begin to charge, and the light went off. 14+ volts at the battery. I made two short trips. Now the light's back on, and I'm only getting 12.25 volts back to the battery.

What else can be wrong? I'm running out of ideas.

[john walker's workshop]

did you clean the battery terminals, the battery to body ground connection, the starter connection for the battery cable/red wire to the alt, and remove and clean the ground strap from trans to body? is the alternator grounded with an extra fat wire/ground strap to the top of the engine case?

[Lee]

Thanks for responding.

Yes to all of that, John. But I'll go over it all again. In addition, I just read that there is a ground behind the relay panel in the engine compartment...I'm going to take the panel off tomorrow and check back there.

When this problem originally began, there was a little insulation smoke...it was the ground to engine case. Could this be related to the fried resistor in the regulator?

[starlifter1]

Did you replace the ground wires that got hot? check for continuity? I found a wire on mine that had burnt but didnt show through the plastic covering. also had a new wire that I ran for my MSD box that looked good (NEW) but was broken under the coating
What a headache, I now test wires even new ones

[Lee]

I replaced the wire to the engine case...that's the only one that seemed to be damaged...but even that one showed continuity. I replaced it just because it was getting pretty shabby.

After that, I replaced the ground strap at the battery. I checked the connections on the transmission strap. then I ran a jumper wire from the ground at the alternator to the negative battery terminal and had continuity.

I wasn't aware that there is a ground strap behind the relay panel...I haven't checked it yet.

[john walker's workshop]

i got a whole 1 1/2 volt increase recently by cleaning up the ground strap surfaces at the body, on the trans to body strap. did you actually remove the batt to body and trans to body straps and scrape the surfaces clean, or just check them with a wrench? the red dash light does seem to be 95% alternator related though.

[Hladun]

When you say "alternator has been checked", what exactly did you do? Was it load tested by someone who knows what they're doing? You may have diode/winding problems. Intermitent shorts could fry the VR.

[scottb]

Originally posted by Lee
When this problem originally began, there was a little insulation smoke...it was the ground to engine case. Could this be related to the fried resistor in the regulator?

This sounds like a hot wire that shorted. Am I missing something here?

[Lee]

John,

I cleaned the grounds...and I actually lost some resistance, but that wasn't the problem.

I've had the alternator out and bench tested by various alternator guys in my part of Atlanta three times. They all think it's good. One of them added some solder to a diode.

I've been over the wiring several times.

It's been over two months now, and I'm tired of driving my crappy old '90 Toyota (The Moldsmobile) I'm going to throw in the towel tomorrow and install a rebuilt alternator with an internal regulator.

I wish I could find an old Marchal alternator w/ external regulator, but I guess it isn't to be, for now.

[john walker's workshop]

just get a bosch rebuilt internally regulated alternator and problem over.

[Lee]

I don't know which brand it is, yet. I'll know tomorrow. The guy at NAPA told me it was original equipment, rebuilt by a very reputable company. I'm hoping it isn't Paris Rhone.

[nhromyak]

Sounds like a bad ground and/or a bad diode. Does the light glow at first then go bright?

Check the ground on the alternator and the negative side of the battery for ohms resistance. This will tell you if you have a bad ground between the alternator and the battery.

Might want to check the positive side too (with ground disconnected).

Good luck.

[Lorenfb]

"just get a bosch rebuilt internally regulated alternator and problem over."

- john walker's workshop -

The absolutely worst choice for an alternator of all the Porsche alternators ever used!
The Paris-Rhone alternators used in the '82 & '83 911s and 928s have the highest
failure rates. The 911SC '78 thru '81 had the best one (70 amp Marchal) when rebuilt
properly. Internal regulator alternators in a 911 air cooled engine are NOT a good application.

[Lee]

Thanks Nick, I went over all the wiring again today. It's maddening. It worked for about 20 minutes, and then quit again. I rushed home, took out the alternator, and checked all the wires while they were hot. I also checked the resistance on all the grounds, including behind the relay panel, and the hot wires from the battery. All good. I think something goes wrong when the engine heats the alternator to a certain degree, but I don't know what.

Loren, I almost bought a rebuilt with an internal regulator, but all the extra expense and trouble of modifications convinced me to stick with what I have. Unfortunately, somewhere along the way, my marchal 70 amp was traded in on a Parish Rhone 60 amp with external alternator. I'm having it rebuilt, since nothing else seems wrong. I'm going to keep my eyes open for a marchal.

Thanks everyone. I'll post the results of my rebuild.