silly installation compounded by stupidity = fried alternator

[Greg D.]

I've joined the club... I never really had a boneheaded moment when fixing cars, except when a 993 tried to crush me but now I have in a big way... My car came back from 1+ year of resto with 2 new batteries fitted by the mechanics. I noticed they fit poorly and one was dangerously close to contacting the battery box with the + terminal. Like 2mm close, one bump and boom...

So I did the right thing and ordered 2 correct ones from Lauderdale Electric, sonnencheim or something... Also replaced the aging connectors... That's where I screwed up. I did not question the cable colors... they were red, I bought red, and red = + in my head. The new batteries fit so much better and I saw the terminals were reversed vs. the old batteries I had but that is where I brain farted: I did not realize that on my car, ground cables were red and positive were black, which is reversed from normal (my normal anyway). I went red +, black neg- not questioning that the posts were reversed now and the cables should have been too, and.... sparks galore.... the ground connector got hot, I immediately went WTF and disconnected everything within 5 seconds.. I then engaged my brain and noticed that red was direct to the body so it was the ground... $%#$%$#%$... beginners mistake.

I am pretty sure I fried my alternator. The car starts, runs well on 2 fresh batteries, but voltage remains the same with engine running, not alternator output, and the alternator light is ON when the car is not running. Oh well, if it were an FAA accident report it would read: Crappy battery installation by the mechanics caused the owner to replace batteries needlessly, and wrong cable color did not cause warning signs in the befuddled owner's brain. Owner is a dumba$$ with some mitigating circumstances... ;-)

Apparently I can get the alt. rebuilt for less than $100, probably a diode. Any chance I did more damage in 5-10 seconds ? the car runs fine except for the alt... If I decide not to pull it myself, can I drive 5 miles in the city on the 2 batteries only ?

[304065]

The good news is that the car is mostly analog!

When you say voltage remains the same with engine running, what does that mean? 12.5V before start and 12.5V at, say 2000 RPM? If that's the case, yes, you either burned up the alternator or voltage regulator. Alternator light ON with the car is not running, well that is absolutely normal.

What is voltage at battery with engine off? What is voltage at battery with engine at 3000 RPM?

If this were the NTSB they would acknowledge the mechanical cause and then blame the pilots.

[Greg D.]

>Alternator light ON with the car is not running, well that is absolutely normal.

Not with the key out of the ignition :-) pretty sure that means I fried the alternator. Now I know how a pilot feels when he lands with the wheels up.. Stupid.. But who used red ground cables dammit ? The fact that the car runs well tells me that hopefully nothing else fried.

What I meant on voltage is that I have 12.5 V regardless of engine running or not. If the alternator was still good I should get 13-something... But like I said I'm sure I fried it, I smelled something and it red light remains on with the key out of the ignition.. Hopefully that's just that, some diodes, maybe a burnt wire at the alternator, and I'll make myself sleep at night telling myself the alternator was really old anyway :-). Hmm, can't find the icon for kicking oneself in the ass..

[edmayo]

Don't beat yourself up TOO bad, I've seen that color confusion before. I suspect the last battery installer just went to PEP boys and got a red cable of the right length, and you're right, those were meant for + application. The post size opening of the cable is different for positive and negative posts. The positive post being larger. I guess you know that the correct ground is a copper weave strap, and that originally there was a molded rubber cap that completely covered the positive post. These may still be available, the ground strap certainly is.

[304065]

>Alternator light ON with the car is not running, well that is absolutely normal.

Not with the key out of the ignition :-) pretty sure that means I fried the alternator. Now I know how a pilot feels when he lands with the wheels up.. Stupid.. But who used red ground cables dammit ? The fact that the car runs well tells me that hopefully nothing else fried.

What I meant on voltage is that I have 12.5 V regardless of engine running or not. If the alternator was still good I should get 13-something... But like I said I'm sure I fried it, I smelled something and it red light remains on with the key out of the ignition.. Hopefully that's just that, some diodes, maybe a burnt wire at the alternator, and I'll make myself sleep at night telling myself the alternator was really old anyway :-). Hmm, can't find the icon for kicking oneself in the ass..

Yep, alternator light glowing with the key hanging on the peg on the wall = blown diodes.

What alternator is in the car? Is this the T? Probably has a Motorola with a single D+/61 diode. Anyway, a good core should be easy to find, by that year I think they were using a 55A alternator. If it were me I would source a 55A Bosch and have it rebuilt by someone good (which is defined as: someone who actually rebuilds it with new diodes and bearings, not just spray paint!)

Don't feel bad the Factory used red in the engine harness in the SWB cars when they shouldn't have, DIN 72552 be damned!

[Greg D.]

Thanks guys, for not beating me over the head anymore than I already have... Do you think I damaged anything else ? I checked the car's headlights, turn signals, (radio not yet plugged in, thank goodness), the ignition switch/starter/CDI obviously worked because the car started like normal and ran well, all fuses are OK, no visibly burnt wires anywhere obvious... I'm hoping it's just the diodes and possibly the alternator ground wire as I did smell something electrical burning, briefly... What else should I look at ? Are there obvious electrical components in a 72T that don't like wrong way current other than the alternator ?

I found a local guy to rebuild it, it's not too bad if that's the extent of it. I ordered rubber post caps. For now I am going to rewrap the (#$@#$) red ground cable with black tape, and put red tape on the currently black positives cables ;-) Thought about the Porsche ground straps but they look really short and I'm not sure they will reach the sonnenchein's posts, I have to measure that...
What really bugs me is I spent $400+ to remedy a dangerous situation and...made it worse and more expensive..

PS: just got Pano and noticed Ed Mayo is answering early 911 questions. Cool, hadn't noticed that before..

[304065]

Let's think about what happened

Normally the alternator diodes only conduct current one direction-- so power cannot flow from the B+ through the stator to ground. On the other hand, when the rotor induces a flux in the stator when it zips past, the positive side of the current flows OUT of the diode to B+.

When you connected it backwards, you basically put a lot of current on the ground side of the diodes, which have little resistance to flow in the direction toward the (new) ground. So you see a short across the diodes, which can't take that much current, and they get too hot and fail.

You didn't turn the ignition on, so I think the CDI is OK. The lamps, etc., are independent of polarity. Your tach is switched with the ignition also, so it should be OK.

Buy the correct copper braided straps, they fit fine with the sonnenscheins, which are dimensionally the same as the lead-acid type. And you are smart to use the positive terminal caps.

Of course you should test everything once the new alternator is in, and make some short trips before you make long ones.

[WCB4]

Wait are these cars not postive to ground anyway? It slowes me down thinking every time I reconect my battary and/or jump start. I store my cars with out the battries hooked up, since no power avilabale for my battary tender.

[edmayo]

Greg, the main battery cables are black, the power wires to the fuse box are red. As you can see the correct ground strap is long enough, and you can see the molded rubber protector on the positive post. This is a Sonnenschein battery in camo mode for concours. By using the woven copper ground strap you can't confuse post hook up. You KNOW that is ground!

Uhh Bill, negative ground, that has been pretty much universal since the mid fifties, radios work better that way, or at least that's what I was told at the GM training center back in the sixties!

[Greg D.]

I have had a starter issue once, since this happened and the alternator got repaired. I think it's unrelated because by and large the starter works, but one time it just gave me that "clonk" and no start. I had that on my ex-83SC too, so I knew to rock the car a bit and it worked... But I'll have that replaced too... Found out as well that I have a permatune on that car, it's not as stock as I thought it was... I've installed new battery ground straps, correct ones, and also capped the + with rubber.
Thanks again !!