alternator or voltage regulator
 

The other night I was driving my 1986 560sl and a series of electrical malfunctions occurred; the radio switched off, then the "antilock" light came on followed by the "light out" light illuminating, followed by dimness of all electrical and then the car quit. I took the battery out of the car and had it charged and tested. It tested good and with a full charge had the system checked. With the engine running, the voltage reading off the battery with no electrical load was 12.8 volts. This points to an alternator problem, correct? I was wondering about the voltage regulator, could that be at fault? Any suggestions would surely be appreciated. Thanks. Rob Thomas

At times, the alternator brushes (inside the regulator), will fail and cause this condition. If you remove the regulator and the contact portion of the alternator armature looks good, I'd just replace the regulator.

I have had it tested again. It showed 13.6 volts while engine running and I took alternator out of car and had it benched tested and it tested 13.6-13.8. I took the regulator off and the portion of the alternator that the regulator rubs against looks worn but I cannot tell if it is excessive. In summary, it seems to be intermittent. Should I still try the new regulator or a new alternator? Thanks. Rob Thomas

Wouldn't the testing of the alternator as good rule it out? The last man holding the stick is the regulator.

I would think so but the one wrench in the entire troubleshooting process was the "bad" test of the alternator in the car. So far, two tests were good, one bad. I will try the regulator. Thanks.

Rob - what kind of traffic were you in when the problems started. On my E320 my alternator was going out and I only noticed it when I got into heavy traffic with alot of idling around. Same symptoms - radio turned off, etc and I think it went into "limp" mode because of lack of acceleration. When out on the open highway at 55-60 there were no problems.

Replaced the alternator and everything is fine after that.

I was on the highway doing 55. Thanks.