I have a '91 Ford Sierra Saphire 2.0 OHC (pinto). Have been struggling with having no charge for weeks now. I've tried two different alternators, had one of them completely rebuilt by a professional, so alternator is not faulty.

Every time it comes down to the voltage regulator breaking. If I replace regulator, alternator charges for like another 5 miles, then voltage regulator dies again. (I've already repalced it 3-4 times, while trying, I pay 10$ for every possible solution :/ ).

I've double checked every single connection (alternator B+ -> battery, alternator D+ -> dash, engine -> chassis, battery negative -> chassis, etc.), I have solid Earth everywhere I need to have (at least according to my multi-meter).

Haven't had the chance to try another battery. Can a bad battery in any way cause serial voltage regulator faults? If not what else can?

  • Does the battery have enough capacity to start the car?
    – Paul
    Commented Jan 8, 2015 at 20:55
  • Initially yes(if I charge it with a charger), then obviously without the alternator charging it discharges, and eventually it won't start the car.
    – galingong
    Commented Jan 8, 2015 at 21:07
  • Have you tried disconnecting the battery from the car, charging the battery on a smart charger for 24 hours, then leaving it off of a charger for 24 hours, then check the voltage? Or at least bringing it to an auto parts store and let them test the battery with a tester?
    – Paul
    Commented Jan 8, 2015 at 21:21
  • Actually I haven't. My first thought was borrowing a known working one and try the thing with that. As far as I know a bad battery does not necessarily leak voltage, nevertheless I should've already tried it.
    – galingong
    Commented Jan 8, 2015 at 21:50
  • If the battery holds a charge, then for certain it doesn't have a short. If it doesn't have a short, then it is unlikely the electrical problems you are having are caused by the battery. Even if it does have a short, it is a near impossibility that it is causing the problems you are having.
    – Paul
    Commented Jan 8, 2015 at 21:53

1 Answer 1


From a theory perspective, I would say it is nearly impossible that a bad battery, all by itself, can cause an alternator to fail. The only condition I can even think of would be if the battery developed a short, but even for that to cause the alternator to fail, there would have to be some other problem in the system, such as a bypassed fuse or something of that nature.

  • You were correct, the battery is fine. I can't indentify the problem even at this point, when everything is working fine. I replaced a bunch of cables, sanded every connector and ground point, alternator was known to be working. The only advice I can give to people with similar problems is to tear the whole thing down, clean up everything possibly related and reassemble.
    – galingong
    Commented Mar 8, 2015 at 17:05

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