Alternator fire...cause???

[Formerly Steve Wilkinson]

Installed a new Valeo alternator in my '83 SC, from Pelican. Double-checked my connections, buttoned everything up, turned on the master in the trunk...and by the time I got into the seat to start up, there was smoke coming out the engine grille. Got the master off, needed the fire extinguisher (Halon, fortunately) by that time, since there were by then flames inside the engine cover from burning insulation.

Before you tell me I hooked it up wrong, I didn't: Big red wire to the post marked +, two brown ground wires to the one marked - and the small green wire to the terminal at the bottom of the alternator.

Was the big battery wire touching something it should have? Nope. It's really not possible inside the plastic air-deflector cone anyway.

Did I have a fault somewhere along the battery wire elsewhere, that was grounding? Nope. the fire was right at the alternator (which is a mess, of course, and I assume NG).

Question: Is it possible for a new alternator to have some kind of internal fault that would cause this dead ground? The short ground wire from the alternator to the crankcase was completely melted through, if that means anything.

[Early_S_Man]

Stephan,

Worst case I have seen is shorted rectifier diodes in both positive and negative arrays ... would drain a fully-charged battery in 30 minutes; it was not quite enough load to catch the wires on fire, but a heavy load, definitely.

Unless it was damaged in transit, you would almost have to suspect a wiring error inside the alternator. I don't know if it is physically possible to switch the positive and negative arrays, but that is what it sounds like.

[Formerly Steve Wilkinson]

'ang on, 'ang on, as Eric Clapton said.

I think I figured it out, but I'll leave this post up as a cautionary tale to slink into the archives for anybody else doing a future alternator changeout.

When I pulled out the torched alternator, after disconnecting the air shroud and the electrical lines, I briefly noticed a tiny 8mm lock washer stuck inside the alternator--can't even say at this point exactly where it was, probably between the windings and the alternator shell, but I was half crazed at the moment, having just put out a fire--and at the time, I thought to myself, "Better dump that outa there before it goes deeper into the alternator, I must have dropped it while disconnecting something..." It fell out as soon as I turned the alternator/shell unit upside down, and I didn't think any more of it until now.

Truth is, it probably was there from some moronic carelessness _before_ I installed the new alternator, and it shorted everything out.

So be careful, there's a lot of constrained-spaces work that goes on when installing an alternator and connecting the lines and then the air shroud, and if a washer or nut goes astray, make sure you know where it went before buttoning up the installation.