Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Roger with the battery installed backwards

Everything seems to work except the alternator isn’t charging the battery now. Tom and Ray suggested to take the alternator to a parts dealer who’ll test the alternator in their test fixture.

If it tests bad, the problem is most likely one or more of the alternator diodes has burned out. This problem can easily be repaired. A fix-it-yourself-handiman type could do it themselves. But the easiest way is to take his alternator to a local auto-electrical shop for fixing. Either ask a local mechanic where the closest shop is, or look in the yellow pages.

This idea will work but it’s usually more cost effective just to buy a rebuilt alternator. Same goes for the starter if it goes bad.

After I was hit by a Grayhound bus one night in my little Sumbeam Imp. My car sat for 6 weeks while a new quarter panel was shipped from Scotland. Of course the battery was dead and they had jump started it.

They give me the car back and I got about a block when it started losing power and smoking. The faster I went the brighter the battery light. I kept it going long enough to get back to the shop where they tried to tell me all they needed to do was to reverse the battery cables. As I watched that is what they did. It resulted in clouds of smoke. I just looked at the manager and said "New battery, starter and generator along with anything else that shows up later. They agreed and I got that neat Triumph to drive for another few weeks while they got the new parts.

I suggest you get them to agree to say a 60 day warranty on any electrical parts. Get it in writing.

@missileman … good point. However, I’ve recently had some problems with rebuilt starters not working right out of the box, specifically foreign-shop rebuilds. It’s frustrating to go through the effot to install one, and find it doesn’t work. If the caller does purchase a rebuilt one, he should have the parts place test it on their machine to verify it is working correctly. And if the cost for a rebuilt is more or less the same as having the existing one fixed at a local shop, within $75 say, and the alternator was working fine and wasn’t making any weird noises before all this happened, I’d look for a local auto-elec shop myself and have them fix it.

jump starting or hooking a battery up backwards will have different results in different cars. Some cars will blow a bunch of fuses, other it can blow a bunch of fuses and modules. If all you got was a blown alternator consider yourself very lucky. Before you take your alternator our for testing check all of the fuses, including the mega fuses. Your should have a fuse or two that go between the alternator and the battery.

@JosephEMeehan … that’s an unusual story. You’d think if the battery polarity was reversed, the car wouldn’t run in the first place. I guess it is possible with an older car with a simple breaker points ignition system and a mechanical voltage regulator and DC generator (which doesn’t use diodes) it might run with the battery polarity reversed. Maybe they accidentally reversed the polarity when they did the jumpstart and it temporily charged the battery w/backwards polarity.