Mercedes 190D Turbo Alternator


The wife’s mercedes one day decided not to charge anymore. So like anyone that hates paying someone to fix stuff I surfed to autozone to see how much this was going to hurt. After seeing almost $200 freaking dollars for a 70 amp alternator I decided I’d look around a little more…..

Seems the Bosch alternator on the car has a built in voltage regulator. Since she had driven thru some standing water right before it failed I figured that would be a good place to start with. Plus it wasnt but $40. When the new regulator arrived I noticed the brushes were part fo the regulator. Thats a good thing.

So I went looking for a walkthru on building it. I found this.

Also since sites like to disappear from time to time Im reproducing the site here. Again I didn’t write the following its from that link, I believe in giving credit where credit is due.

Mercedes Voltage Regulator Install

This is one of those items that most people never even check, until its too late.  The voltage regulator fits into the rear of the alternator and over time will wear to the point the alternator will not charge the battery.  The Mercedes alternators are some of the most durable I have ever seen and will last many years.  However failure to check this simple item, can leave you stranded on the side of the road.  Poor battery charging will not stop the engine from running on the older models without computer control, however every electrical accessory and component will fail to operate once the battery is discharged.  With the alternator not charging properly and the battery drained, nothing electrical including things like brake lights, turn signals etc. won’t work.

Checking your voltage regulator is very easy to do and is a “must do” item if you have gotten another Mercedes.  Keeping a spare in the glove box is also wise, especially on those long road trips.  I had a customer tell me the car was only charging 2 volts and was told the alternator needed to be repaired.  Since I had a spare one at the shop, I told him to bring the car over and I would take a look.  Well after removing the voltage regulator I could see why it was not charging.  The carbon stacks were slap wore out.  5 minutes later and new voltage regulator was installed and he was one his way.  Always check and replace this item before scraping the alternator.  So follow along as I show you how to check the voltage regulator.

I did this pictorial with the car up on ramps because its easier to do and I am a big dude and like lots of room.


This is what the alternator looks like from under the car.  As you can see the voltage regulator is held in with 2 Philips screws.



I use a stubby Philips screwdriver to remove the 2 screws…..


Then just pull the voltage regulator out and this is what is left.  You can barely see the shaft the carbon stack rides on.  They will be nice and shinny….


Here is the voltage regulator showing the 2 carbon stacks.  They have lots of like life in them.  New voltage regulator carbon stacks  are not much taller than this one.



You can see the concave shape the end will have due to rubbing on the shaft.

If your voltage regulator is about 1/2 as tall I suggest replacing it.

Now either reinstall your old good regulator or install your new one.  Snug up the screws and you are done.  Test the battery for proper charge and also the output of the alternator.  Many auto supply store will test it for free while its on the car.  13-14v charging is the range you want to be in.


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