1973 W115 charging issue
 

Hey everyone:

New to the board. I've lurked a while but finally registered so I can get some of your educated advice.

My Mercedes is a '73 220D. Slow as a bicycle but I love it...it's quite a car.

However, I had my first issue recently. I was going down the road to one of my job locations, and noticed the GEN light on. Needless to say, I wheeled it around toward home since it was getting late in the day.

Quick check with the meter shows no charging. The light is on, but not brightly...dims the more the engine is revved. Here's the odd part- with the ign on but not running there is no GEN light.

I left it sit a few days with the battery cable off out of an abundance of caution and the next time I start it up, the light was operating as it should and it was charging.

Get in it a day later to drive somewhere and it's back to the dim light on all the time again.

This one has the regulator on the fender apron and tapping it makes no difference.

Thanks for any help.

I had a bad connection at the alternator in my 1968. The Generator light would sometimes stay off for days. Other times it would be brightest at idle, and dim at higher rpm. I cleaned the contacts on the alternator and the plug a few times which fixed the problem, but it seemed to come back some weeks or months later. Finally, I bought some conductive grease that is supposed to suppress oxidation between connectors (I think it was designed when homes had aluminum electric wiring) and it has solved my problem. So, this may have nothing to do with your problem, but it sounded vaguely similar so I wanted to share. Good luck.

Well I dug into this deeper.

The alternator itself had a couple issues that I corrected....it was moving around on the mount which appears to be common from what I've read. Also the ground strap had broken broken off.

Unfortunately neither of those fixed it.

I let it run at fast idle for 15 minutes or so with no charging taking place. Then all of a sudden the light turned off. I measured it and the alt was charging, but just weakly..with lights on it was about 12.9v and with them off it would start to approach normal at 13.6v.

So, a couple more questions-

I know on the later versions the brush/regulator assembly can be removed easily. This one is the older version with the separate regulator...so what is required to get the brushes out? I'm also guessing I'll be detaching that A/C compressor for sure to get to it.

I'm think if the alternator has to be cracked apart to get to the brushes, I'll just drop it by a reputable repair place here in Huntsville and have it gone through.

Thanks for any help.

Or just pick up a "newer" one which has the diode pack/regulator and rewire it to work. Just takes three wires. Battery, field and stator (light) wires.

Sorry to take so long to update this, but you were exactly right.

I started the engine, carefully snaked my hand down to the alternator and when I pushed on the plug I heard the engine idle drop as the alternator kicked in.

It's acted up a couple more times, so evidently it needs the same sort of attention yours did. Thanks for the help to everyone.