the dash lights on my 81 240 volvo started coming on as I was driving home from a long weekend in the mountains this evening. If I put it in neutral and revved the engine they go out, also if I give it enough gas to shift to a lower gear the dash lights go out but then they came back on after a couple of miles. I raised the hood and made sure none of the belts were broken and it doesn't do the usual dimming and brightening of the headlights indicating a bad alternator. So far it doesn't seem to have an idle problem or any other problems. Thoughts!
Every time I get this on my 740 or 940, it's almost always that the brushes on the regulator pack are worn down and starting to lose contact with the armature of the alternator. I go to the dealer (or your favorite parts source), and for under $100 (can't remember, $60 or $70), I buy a new regulator pack with brand new brushes. I disconnect the battery, remove 2 screws, remove and replace the pack. Because this is a common wear item for me, I always carry a spare in my car. The reason is that usually when this happens, you only have a short time before the battery loses its charge, then the car won't run.
I did have one rare occasion where one of the leads going to the alternator broke off. We rigged it back on, and push started the car (standard) and made it home. Another time, the adjuster bolt broke and the alternator was lose in its mount, and the belt tension was way loose. That was my fault for not tightening everything after changing a belt.
If the alternator has mega miles on it, the armature may be too worn to accept the new brushes. Then you must replace the alternator. But, I've done the regulator pack numerous times with great success.
I haven't had a 240 in over 10 years, but according the the Haynes on my shelf, it has a brush pack with a separate regulator. So, you should be able to replace the brushes.
I tie a piece of cotton around the brushes so as not to chip them then break the cotton once the brushes are in place .This is because Murphy and his laws live in our house . If you tap the alternator you might find the brushes make contact for a bit but not for long .Your radio most likely will be full of static due to the brushes arcing .
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