The alternator light is on constantly for the last day. I imagine that the alternator is shot. Should I also test the voltage regulator? I understand they can go bad more frequently than the alternator. Most importantly, I have a multimeter but need coaching in testing both components. Can someone give me a walk-through?

Thanks


Mike

mccan,

The chances are the brushes on the voltage regulator are worn down to the point where they no longer make adequate contact with the alternator rotor. This is very common. They are easy to remove and replace, easiest if you get a new voltage regulator as it will come with new brushes. Others on the site have reported replacing just the brushes for a couple of dollars and some time. Do a search on brush replacement or voltage regulator replacement. Lots of data. Good luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Replace the regulator and brushes first ($15). They go in as a unit to the back of the alternator with 2 screws. A 15 minute job.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

mccan,

For some reason the way the electrical system is designed, the alternator light usually does not turn on when the brushes are worn out. So brushes may not be your problem.

But if it is worn brushes, you can just replace the brushes. I replaced the brushes in my alternator about 120,000 miles and it has been working ever since.

If you put in a new complete v-regulator brush combination, put brushes in the old assembly anyway and keep it as a spare. You never know when the new one will fail and you can replace it with the old assembly. I always carry a spare when I go on long trips away from home.

P E H

Thanks Gents.

PEH, when the light comes on have you is the alternator generally shot?

Do I need to go to an alternator shop for brushes?

Thanks again.

Probably, but maybe a good hardware store will have them. You can go to Fastlane for the combination of regulator and brushes

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Brush replacement, pretty girl included (with Bert).

Thomaspin:
A picture is worth a thousand words. A picture and a few words is worth ten thousand words. Great explanation.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

mccan,

Brushes are not available from Fastlane or Parts shop, at least thats what Phil told me. You can get from MB dealer, they are not too expensive. Any Bosch dealer should have them or can get them.

The reason I said the ammeter light does not come on is that mine didn't when my alternator stopped working and I remember that some on this web site said the way the circuit is made, if the brushes are worn out, the light doesn't come on because of the way the charging circuit is designed.

If a new brush/v-regulator doesn't fix your alternator, you probably need a new or rebuilt alternator. You might have it checked at a Bosch shop if there is one is near you.

P E H

Pindelski,

You are my freakin' hero. I salute the man with the temperment and approach that makes for your kind of thoroughness and what looks like genuine enjoyment found on your site. Way back when in college I was a radio jock and one of my cohorts was a walking encyclopedia of rock and roll. Anything he didn't know, he knew where to look to learn about it. You are that kind of encyclopedia. The guru. The Diesel Lama...

Oh, and thanks for helping me discover a friend in a machine and a way to learn some new things about myself and my capacities.

I'll be picking up a new regulator tomorrow.

Thanks for the nice words, but I have to add that there are many here far more expert.

I confess that now and then I toy with the idea of selling the 300SD. It's been a 16 year relationship. We all get bored. The 560SEL is everything the SD is not - powerful, sophisticated, far safer, quiet, a haven after a busy day. And the leather still smells great!

But it does lack the one thing all diesels have.

Character.

Thanks again.