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Discussion Starter #1 (Edited)
Any part in a car will fail if you wait long enough, but some parts very rarely cause trouble.

One of these is the alternator. Its bearing should last well beyond 200k miles, unless run with belts overtightened for an extended period of time; the diode pack (rectifier) should also last forever, barring any major shorts in the charging circuit. The regulator, also, may never need replacement. But the brushes, because they are physically consumed, are guaranteed to wear out after 150k miles or so.

This happened to my 1990 900S yesterday, at 160,400 miles.

I could not find replacement brushes in the short time I had to get the car on the road again; the stealership didn't sell them as separate items, but they had the regulator assembly (complete with brushes) for $67. I bought an aftermarket version from NAPA for $35. At this price, I was happy to have a new regulator as well as new brushes--and no soldering needed.

The regulator/brush assembly is tough to get at, but I replaced it with the alt. in the car, and without removing any other components. Here's how:

(1) Disconnect battery. Carefully pull off the connectors for the alt. D+ wire (the really thin one) and for the oil-pressure switch. Examine them carefully to make sure they're securely attached to their connectors (no broken strands)--they are disturbed every time the oil filter is changed, and have been known to break off. Move these wires out of the way.

(2) The outer of the 2 regulator mounting screws can easily be reached with a short Phillips screwdriver, but access to the inner one is blocked by the oil-pressure sender. You could loosen the alt. mountings and remove the belts so you can swing the alt. away from the block, to give screwdriver access, but I loosened this screw by clamping long-nose visegrips on it. Then, use your left hand to undo it with a normal Phillips screwdriver. Now undo the outer screw, and pull the regulator down and back to remove.

(3) Start the refit by holding the new regulator in your left hand, and install it low down in its opening in the alt. backplate so the brushes don't snag on anything. Now, slide the assembly upwards--you will feel resistance from the brush springs.

(4) The screws have ridiculously fine threads, so you need to "feel" them as they bite when reinstalling. With your left hand holding the regulator in position, slide your right hand down between the backplate and the coolant bottle hose. Now fit the inner screw--you may have to use the tips of both index fingers to start it turning. Finish with the screwdriver, but don't fully tighten yet.

(5) Now, try fitting the outer screw. You may find, as I did, that the regulator's mounting hole doesn't line up perfectly with the hole in the backplate. This is because the regulator's mounting plate is fouled by the plastic insulator of the alt.-to-starter cable. You could remove the reg. and file its mounting to shape, or ream out its mounting hole. But I just found a sheetmetal screw of the same width and length as the mounting screw. The new screw had a point and a coarse thread, and I easily installed and tightened it. Problem solved!

(6) Refit the 2 wires pulled off earlier. Reconnect battery. Turn ignition on, and make sure charge light is on. Start engine:Ign. light should go out immediately. If so, consume suitable beverage in celebration:)
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