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Re: alternator problems... Posted by RS [Email] ![]() ![]() ![]() In Reply to: alternator problems..., alan evans, Sun, 29 May 2005 16:37:38 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Often what happens with high-mileage (over 150k miles) 900s is that either the carbon brushes that contact the slip rings in the alternator wear down below their service limit or the ground wire that runs betweeen the alternator case and the engine frays and doesn't allow the battery to charge when you have a high electrical load (lights, wipers, fan, a/c, etc.) (howzzat for a long sentence?)
My '88 900s coughed and died during a heavy rainstorm when the brushes were too short.
Does (or did) the alternator light glow faintly when the car was running?
That brushes are on the voltage regulator, which is located on the non-pulley side of the alternator, near the oil filter.
Another possibility is that, if the battery is old, it's lost its ability to hold a charge or there's some parasitic drain like the trunk light or automatic seat belts that don't fully retract, if you have them.
Here's some text on testing from a previous post:
If you have a multitester, do a couple of quick tests: What's the voltage between the battery terminals when it's off? Then, start the car, Turn lights and accessories on, and check the voltage between the battery terminals. Compare that voltage with the voltage between the alternator case and the negative terminal. If there's a difference of more than about 1/4 volt or so, then the ground cable is bad.
It's possible that the positive cable has some internal corrosion that's not visible. Someone posted about that recently. In a climate like this, I think that the corrosion you mention is caused by some leakage around the battery terminal. This might be from the battery's low charge state.
Among other things, it's also possible that the ignition switch is bad, letting some voltage drains remain on when the key is off - but that's a real long shot - we'll keep that thought way on the back burner.
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