Where do I begin to explain? I own a 1987 240DL. I am having occasional electric problems. First of all the stereo only works when it wants to, and all the dash warning lights are on. The altenator will suddenly stop working, all guages will drop, headlights will dim. Sometimes I can drive for an hour, other times only a few minutes. When this occured tonight i tried hooking up a new battery. When the battery was connected the radio suddenly started working (for the first time in 2 weeks). Also when the atenator starts to act up the car runs kinda rough and runs very rich. I have checked all ground wires & the brushes in the altenator were replaced a year ago. The combination of symptoms is the confusing part for me.

Before I started checking eveything you mentioned I thought I should check the wear on the brushes. They were worn nearly out of sight. I cleaned the rust and corrosion off all connections and washers. Everything works like a charm. No lights on on the dash, radio working consistantly. I think that was the problem. BTW I looked high and low for the grey box with the 8 wires, no luck. I do have a black connection with 5 wires though. All wires are good with no signs of aging. Thanks for your help, I will keep your tips close at hand for future referance.

Check this out:

There is a thin red wire attached to a spade lug on the back of the alternator. It is vital to alternator operation.

That wire provides a bit of voltage to get the charging started, after that the alternator becomes "self-exciting". The voltage comes through the amp warning light on the instrument cluster.

If the amp light stays on when the engine is running, the red wire is grounded somewhere that it shouldn't be. And, the alternator is not charging.

What you describe is a situation where that wire is grounded sometimes but not all the time. Common, and usually occurs in the harness that runs under the front of the engine. Hostile environment for wires.

There is a gray 8-place connector on the firewall. Your car uses four wires, not all eight. All four are subject to insulation deterioration and failure. The red wire is one of them, the others go to the oil pressure sensor, water temp sensor (talks to gauge), and the starter.

It is a DIY job to install new re-routed wires, leaving the old damaged ones isolated in place.

Look at that thin red wire, and post back with your findings.

Good Luck,

Bob

:>)