My '86 started running poorly and the battery light would come on when the engine speed dropped under 2000rpm. I did some voltage checks at the battery and determined there is a charging problem since I'm only getting around 11V at idle. Took the alternator out and found the brushes in the voltage regulator to be worn and the slip ring in the alternator also worn, in fact worn right down to the base material. I also found while removing the alternator that the fan housing has many cracks and it should be replaced. So a new alternator plus a new fan housing and I'm looking at close to $1,000. I just want to get through the rest of the season and wait until next spring to spend that much. So what could I do temporarily? I decided that if I could get the brushes to make contact with the unworn areas of the slip ring, the alternator should charge and I might get away with it for a little while. So I cleaned up the brushes, then I added some washers under the voltage regulator to shim it up a bit so the brushes would be relocated. I put everything back together, started the car and viola! Charging at 14.28V at idle! Looks like I may have bought myself a little time. Another bonus, the slight hesitation and jerking I used to get on acceleration is now gone. I guess the car had been operating at less than optimal voltage for some time and the DME didn't like that.
