Charging system problem - PeachParts Mercedes-Benz Forum

ramjensen · #1 11-21-2006, 07:04 PM

OK, I just installed an amplifier on my aftermarket stereo in my 87 benz. I noticed that my warning light on my dash for a blown exterior bulb started coming on then turning off. It did that for a few days, only all my bulbs were fine. Then I noticed my headlites seemed a bit dim one nite, then last nite i barely got home they were so dim, and my antilock brake lite came on and stayed on. I put a voltmeter across my battery and got only 7.5 volts with the car running. While performing this test I noticed that like an idiot I had failed to hook up the heavy duty power wire for the amplifier to the positive battery terminal. Instead the ring terminal on the end of the wire was just sitting against the positive battery terminal. So, the amp worked, but I think that by trying to drive a 225 watt x 2 channel amp through this very poor connection, I may have done something bad to my charging system. Any ideas? I put a trickle charger on the battery last nite and it did appear to take a charge. I just tested the battery with the car off and got 13.6 volts. I started the car and tested again, this time 12.7 volts with no accesories on, just the dome light. So, the charging system is nonfunctional. Isn't there some type of low voltage protection circuit, maybe I blew that or fried the voltage regulator or alternator? Please help, I am an idiot when it comes to electricity (in case that's not already obvious)

SD Blue · #2 11-21-2006, 11:49 PM

Check/refurbish grounding connections for Batt.-Chassis and Chassis-Engine. Also, make sure there is no corrosion at the alternator terminal strip on the passenger fenderwell. See if this makes a change.

If not, then the voltage regulator or alternator diodes may be fried. To check the alternator diodes, put your meter to Volts AC, with the engine running, and it should be less than 1 VAC.

ramjensen · #3 11-22-2006, 08:04 PM

Sam, where do I put the leads of my voltmeter to test the alternator diodes? Also, I have been having an intermittent problem with my car idling rough when cold. Could this be a symptom of a faulty ovp as some posts suggest? I checked the fuse on my ovp and it was fine, maybe the unit itself is bad. Would a faulty ovp cause my charging system to malfunction? I plan to pull the voltage regulator tonite to check my brushes...

SD Blue · #4 11-22-2006, 10:53 PM

Put your leads across the battery terminals, with the engine running, and in Volts AC.

For rough running while cold, I would suspect a glow plug, or two, is not up to spec. They can easily be checked by pulling the connector off the glow plug relay and measuring the large pins to ground. Should be about 1 ohm I believe.

I'm not sure what you mean by "ovp"? Do you mean the glow plug relay? Sometimes when it hangs up, the battery can discharge rapidly. Usually indicated by higher than normal temps. I always wait till I hear the relay contacts trip before starting.