The Stovebolt Site Forums The Shop Area The Electrical Bay Ignition/Alternator gremlins, or just bad luck?

I have a '52 GMC 3/4 ton that I recently put a Chevy 350 in. It has a stand alone HEI distributor on it. I've had a couple of issues with it and I'm wondering if there's an electrical expert that can tell me if I'm doing this right or if I'm doing something wrong.

First, the HEI just quit a week ago, leaving me stranded. When I took it apart, the rotor was melted so that the metal pieces came out. It looks like it melted from the current passing through it. The brand was Pertronix. I replaced it with the stock GM rotor and it works again. But I'm concerned with why it melted. That's the first problem.

The second problem is that I had wired the BATT terminal of the HEI directly to the battery connection on the alternator using a 10 gauge wire; but it's wired through a relay that is triggered by the 12V switched ignition. Then the alternator is connected to the battery with a 10 gauge wire also. This worked fine for awhile, but the alternator fried. That's right, stinky smoke coming OUT of the alternator, and it no longer puts out a field.
It's a 120 Amp alternator (an old one), and I am going to have it rebuilt. But this is the second failure in as many days, and is it coincidence that the HEI has its battery connection routing from the alternator and both had failures, or do I have that wired wrong?

I know on modern cars with HEI, they always took their BATT signal through a fusable link from the starter. But then the starter has a wire going to the alternator too. So what's the difference? Electrically it seems to be the same point to me.

So are they related as I'm afraid they might be? Or is it just a lousy coincidence and I'm wired correctly?

Please advise.

Hy Hot Rod Dad, I'm a retired mechanic, not an electrician, but it seems to me that once your relay is activated, you now have two paths to ground for all the alternators output. One through the distributer, limited in flow only by the current carrying ability of the relay contacts, and the other limited only by the size of the wire. As you stated the factory used a fusable link in the circuit to the H.E.I., did the H.E.I. installation instructions talk about fusing the circuit? If it were me I would take the power from the horn relay battery terminal or the starter battery terminal, and stop funneling alternator output through the distributer. As to the alternator failure, you said it was an old one, maybe the field windings, or stator windings finally shorted, hope that helps.

DAD,

You are using the terms HEI and Pertronix loosely...what distributor do you have? A 350 could have a GM HEI but that wouldn't involve any Pertronix. A stock GM points distributor could be retrofitted to a Pertronix system, but it would be called solid state or breakerless, not HEI...this is what I think you have, a old points distributor with neat new Pertronix guts.

I haven't done this swap so I don't understand what you mean when you say you replaced the rotor with a stock GM rotor...who's was the other one, the one that melted?

All I have done is ask questions..sorry. I cannot see any problem with the way you have it wired up. I would write the melted rotor up to some type of mismatch if it wasn't a GM product that matched the cap.

I assume your alternator is a single wire unit as you didn't mention the additional DA wiring. If it is a three wire unit, is there something rotten with that wiring? From the info in your post right now, I can see nothing but a coincidence, although I'm not a firm believer in coincidences.

Stuart

While I was converting from a points to breakerless ignition distributor I was told never to use solid core spark plug wires. They will eventually burn out the electronics in the distributor. You need spiral core or spiral wound graphite core wires. Just a thought.

Atomarc, Pertronix DOES make an HEI rebuild kit, with a 50,000 volt coil, an ignition module, cap, and a rotor. I bought the Pertronix kit for two reasons. The first is that I used Pertronix electronic ignition conversion kits for breaker-type distributors many times with happy results and I trusted them. The second is that my truck is red, and the red cap matched my truck (admittedly a weak reason, but still...).

It is an early GM stand-alone HEI distributor. It is just rebuilt using this Pertronix kit. When the Pertronix rotor melted, I went into my storage shed and dug out the original GM rotor that I had for it before rebuilding it, and put that on. That's what I meant by that.

The alternator is a 1986 IROC-Z unit, 120 Amp, with 5 rib belt pulley. I bought it for my IROC that I no longer have, but since I'm planning on reinstalling the IROC's TPI fuel injection system, I wanted to use the IROC's alternator as well, since it will plug into the harness. And yes, I do still have the IROC's HEI distributor, but chose the stand-alone HEI for now since I am currently running a carb.

I will be taking the alternator to the electric shop to rebuild it tomorrow, and I will also ask them this question and see what they say about the connections. If I run the BATT wire to the starter instead of the alternator, but the alternator ALSO has a wire to the battery via the starter, then electrically it's all the same I would think. Still, I'm going to make sure before I fry another alternator. I'll post here what they tell me.

Yeah it was just bad luck. I asked the technician if I had it wired wrong and he said it would be much better to use the battery as a source for the HEI and not the alternator, but that no, the alternator just picked that day to die.

I found out the alternator was out of a 1985 Buick Electra and was a 108 Amp, but he souped it up to a 120 Amp while he was at it, which is cool. Now I can run A/C and an electric fan if I ever want to.

So anyway, I'm going to rewire that circuit while I'm at it.
Thanks for all your help.