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MG MGB Technical - It's official, I'm an idiot.

Well, we've all had one of these moments. I suppose that since I finally just completed my head replacement after a rebuild, it was time for me to screw up something else. So I think I've fried my alternator.

I took the car out for a trip over the hill to Santa Cruz, both to enjoy the nice weather and to put the car under a full range of load conditions (after which I was going to retorque the head). Unfortunately, I turned my lights on for the wooded sections of highway and forgot to turn them off when I parked. When I tried to depart some hours later, the battery was dead.

But that's no big deal you say. Ahhhh....but it is for me. So, I enlisted the help of a friend and proceeded to go through the usual jump start procedure: red cables to red terminals on both cars, black to black on on my friend's car, and black to the frame of my car. This would have been fine but for one small fact--the leads on my battery are reversed.

This is where it becomes clear that I'm an idiot. You see, when I resurrected my car about a year ago after a 15 year period in our garage, I found that the car had been mysteriously hooked up for positive gound. Since it's a 1974.5 mgb roadster, this was pretty unusual. Of course, this arrangement had killed the previous alternator (which was a royal pain to replace). Anyway, when I put a new battery in, I tried to change the battery leads around so that black would go correctly to negative and red to positive. But, after much penetrant and struggle, I simply couldn't remove one of the leads. So I gave up and decided to just hook it up with the wrong colored wires in place. I promised myself I'd remember this reversal in the future.

And I did remember it, but only after I began to see smoke emanating from under the hood. I quickly disconnected the battery and opened the hood to reveal my alternator smoking like a steam locomotive. At this point I figured my alternator was shot; so I had the car towed home.

But apart from sharing my idiocy with all of you, I have a question: how can I tell if my alternator is really dead? Is it possibly that it might still work?

I charged the battery at home so I could get it into the garage; and curiously the red charging light went off as usual. I'm planning on checking the output voltage with the aid of a friend's voltmeter tomorrow. Is there any other way of checking whether the alternator works or not?

Jeremy
J. Palgon

Hi Jeremy.

You aren't an idiot, you are a human.. lots of ppl have made much bigger and more devastating mistakes.

May I offer you a tip for the future that works for me ?.. if I need to leave something in a state where it might be hazardous when I come back to it I always leave myself a big, non-lose-able note in the appropriate place. This is common practice in commerce, industry and military circles (or at least the truly professional ones !).

In your case I would have written a big note, put it in a plastic sleeve and secured it to the top of the battery cover.

The alternator's diode pack has been over-stressed, as has the regulator pack, and the smoke suggests that the wiring insulation has been burned.
I would definitely fit a new alternator. Even if the old one does still work it is 'walking wounded' and could let you down at any moment.
We all know that moment is usually when you are far from home, at a time when everywhere is closed, dark, raining, and you have some pressing need to be somewhere else !.

Don
Don

Don't worry, Jeremy, I think all of us have earned "idiot" status at one time or another. At least all the honest ones amongst us.

Even if it seems to work OK, for your own peace of mind, I'd replace it.

http://cgi.ebay.com/ebaymotors/MGB-MGB-GT-used-Alternator-in-Exc-condition_W0QQcmdZViewItemQQcategoryZ34202QQitemZ4642003409QQrdZ1QQsspagenameZWDVW

Good feedback and (so far) a good price.

http://cgi.ebay.com/ebaymotors/96-Amp-Delco-Alternator-for-MGB-MGC-Triumph-NEW_W0QQcmdZViewItemQQcategoryZ34202QQitemZ4643346592QQrdZ1QQsspagenameZWDVW

Or go for an upgrade.

or:- www.AAA.com

Derek Nicholson

Of course, the second item is more than likely a Saturn alternator available from Advance Auto for $69.99!

http://www.partsamerica.com/ProductDetail.aspx?mfrcode=AGA&mfrpartnumber=81073&parttype=11&ptset=A


Derek Nicholson

The opposit is also true. When we got my 67, it had been converted to Neg. Ground but the PO did not mark it. Yep, you got it, hooked it up as a positive ground to jump start the car and fried the diode.

I now have NEGATIVE ground stickers under the hood, on the battery tray cover and as Don recommended, A large plastic tag on the battery to remind anyone else.
Bruce Cunha

Hey guys,
Thanks for the words of support. It's really not that large a gaffe. But after all the things that have gone wrong with the car just as a matter of being an MG, it's annoying to have caused damage myself.

Actually, I distinctly remember taping a large label to the top of the battery (as Don suggested) when I closed the box up a year ago. I guess it didn't stand the test of time, as it is no longer there. I think if I hadn't been so hasty, I would have remembered. It's just so natural to attach red to red and black to black.

My thinking is in line with everything that has been said. Even if it is working, and it looks like it is, it may let me down at an inopportune moment. Thanks for the ebay link, I was already on top of them. Actually, I emailed the guy from whom I bought my current rebuilt alternator on Ebay for $35 (including shipping!) a year ago. He claims to have another one available, so I'll probably purchase another one from him.

Quick question, are all negative gound Lucas alternators for the MGB alike? The Moss Catalog shows different models for different years. My Ebay source says I need model number 14050. Is this correct. I don't recall how I came to purchase my last one, but it was from the same guy and it was correct; so I'm assuming he's right.

Next up, the dreaded installation. Last time it took me three hours, the help of two friends, and a ton of brute force to get it in place (that blased adjuster is virtually useless). Here's hoping it's easier this time.

Jeremy
J. Palgon

Jeremy - I think it's called paying one's dues, not idiocy (although it maks you feel like one). We've all been there at some time or the other (like putting a jack screw through the gas tank because I left the jack behind the car). Unfortunately, the dues are sometimes quit expensive, but then, you never forget. Cheers - Dave
David DuBois

Mistakes are how we learn. I do prefer to learn from OTHER peoples mistakes but I've done my fair share on my own too! I am going to go home now and make sure I have my battery leads very clearly labeled though :)
Simon Jansen

Alright everyone,
New question. In the process of doing this have I killed anything other than the alternator? I've definitely blown the radio in-line fuse. No big deal there. Anything else? Could I have possibly drained the battery such that it is beyond holding a charge again?

And Simon,
Nice to know that my mistake can benefit people the world over ;-) .

Jeremy
J. Palgon

Hi Jeremy.

You are only likely to have damaged circuits / components that are (1) polarity sensitive and (2) in circuit at the time that the wrong polarity was applied. Things like an electronic ignition would not have been in circuit so should not have been damaged.

Obviously the alternator and radio did fit into that category, hopefully the radio had a reverse polarity protection diode fitted internally and the fuse blew before that diode was damaged.

The only other obvious thing that I can think of is the clock. I understand that some US spec cars had extras to comply with local regulations, not sure about these.

Don
Don

This thread was discussed between 24/05/2006 and 25/05/2006

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