Early car alternator install question - please help :(

ZCAT3 · 11-10-2004, 06:37 PM

The alternator in my 69S was overcharging the battery (almost 17 volts at 3,000 RPM). I replaced the external voltage regulator and it made no difference so I ordered a rebuilt alternator. I went to install it tonight and I fried the positive lead at the battery. The alternator has 3 connections and a ground strap. I replaced the ground strap as it looked pretty grungy. There are 2 wires to connect to 2 of the 3 posts and a plug to plug in the back. The plug is obvious, as was the 2 wires - at least I thought. One of the wires uses an 8 MM hex head nut and there is only one post of this size, so that seems obvious. The other wire uses a 10 mm hex head nut and there are 2 posts of this size. The alternator came with an extra nut on one of the posts so I assumed this was the post to mount the other wire on. I did so but when I went to attach the positive battery cable I got a shower of sparks. So I presumed that I mounted the wire using the 10 mm nut on the wrong post. So I switched this wire to the other post and when I hooked up the positive battery cable there were no sparks. I started the car briefly - maybe 2 seconds and then the power started to go dim and I could smell smoke. I went up front and the positive cable was smoking and actually melted its connector. What gives - this should not be this hard???

ZCAT3 · 11-10-2004, 08:01 PM

So I went through all the connections again and hooked it back up the way I thought it should be in the first place and now it works fine. There is definitely a short somewhere back there. The alternator is now charging the battery correctly - about 14 volts at 2500 RPM, but I am still seeing a problem I had which I thought this might cure. When I turn the headlights on the alternator light glows slightly and then when I hit the high beams the tach bounces around madly. With the old alternator, when I hit the high beams it would usually kill the engine altogether, so this is an improvement. Does anyone have an early car wiring diagram I could get a copy of? This car has been pretty stripped of all non-essentials and there are loose wires everywhere. It looks like I should just go ahead and replace everything that looks suspect (which is almost everything).

Thanks.

deoxford · 11-10-2004, 08:23 PM

Bill,
I can't help with a early diagram, I do have one from a 72, if you want me to email it to you.
Derek

oxfordsearly911@mchsi.com

Rot 911 · 11-11-2004, 05:21 AM

Looks like you might find what you need in the way of a diagram here: Pelican Wiring Diagrams

jpnovak · 11-11-2004, 06:27 AM

WAIT! STOP! There are no shorts. The red cable (B+) does go on the 10mm post. its a direct wire to the battery after it makes a breif connection at the starter. look on teh back of the alt, it is labled for the three posts and clips.

Always disconnect the battery when doing electrical work. Its very easy to short, spark, weld and kill electronics.

RED = B+ (12V, 10mm post)
Black = Df (clip)
Blue = D+/61 (8mm post)
Brown = D- (8mm post and don't forget the alt housing strap although some early cars didn't have one.)

Sounds like you have it working but be careful!

Early_S_Man · 08:13 AM

Bill,

I suspect you may have permanently damaged your alternator when the melted wire incident ocurred ... it may need rebuilding or repairing! You could have easily exceeded 100 Amps through those diodes ... and that may have blown a few! You may now have only one or two of the three phases actually putting out current now. A current load test would tell for sure.

I suggest taking it to an alternator shop for testing!