1985 w126 not charging- 11V at idle. voltage regulator or something else? - PeachParts Mercedes-Benz Forum

bigblue · #1 12-03-2007, 06:22 PM

note- I currently have the instrumental cluster off the car so I have no functional glow plug light.

It's been sitting in the garage for a while. Today I started it, pulled it out for some garage cleaning, decided to let it idle for about 1 hour, shut off, 1 hour later just a click. Jumped it and it fired right up so I put a voltmeter on the battery terminals and only see 11 volts.

Is there a fusible link I should check or can the lack of instrumental cluster somehow be effecting the car's ability to charge? Or should I just assume I have a bad voltage regulator or alternator?

Brian Carlton · #2 12-03-2007, 06:33 PM

Be nice to know what the voltage would be at 2000 rpm with the headlights on and the blower at max speed.

bigblue · #3 12-03-2007, 06:50 PM

Hi Brian
I thought about that, but didn't bother putting a load on it and rigging up something to hold the idle up since it was so low, especially since there currently isn't a tach hooked up.

kerry · #4 12-03-2007, 06:52 PM

I believe the instrument panel does play a role. I have a vague recollection that if the alternator light fails, the system won't charge. I assume same thing would happen with the alternator light removed from the system.

Brian Carlton · #5 12-03-2007, 06:59 PM

Quote:

Originally Posted by bigblue

Hi Brian
I thought about that, but didn't bother putting a load on it and rigging up something to hold the idle up since it was so low, especially since there currently isn't a tach hooked up.

Without any data...........we can just make some guesses at the problem..........if you like...........but, then we'd be no better than the average mechanic who finds the problem based upon the symptoms as provided by the owner.

toomany MBZ · #6 12-03-2007, 07:21 PM

Check your voltage regulator, to see if the brushes are making contact.

barry123400 · #7 12-03-2007, 07:44 PM

If you plug the instrument cluster back in it hopefully should start to charge. Certainly do not try to troubleshoot this problem with it disconnected.

Brian Carlton · #8 12-03-2007, 07:54 PM

Quote:

Originally Posted by kerry

I believe the instrument panel does play a role. I have a vague recollection that if the alternator light fails, the system won't charge. I assume same thing would happen with the alternator light removed from the system.

This could definitely be possible, if the circuit for the light is used to energize the field. I can't tell from the schematic.

bigblue · #9 12-03-2007, 09:55 PM

That certainly makes the most amount of sense. I'll have to get the dash back together first, though now is a great time to learn a bit more about how that charging system works exactly

bigblue · #10 12-03-2007, 10:22 PM

Sounds like you guys were right

New alternator and battery, now what!? 300D Electrical Injustice...

Had I known this could actually do it I would have done a more thorough search first! I guess that instrument cluster really does need to be on there

chetwesley · #11 12-03-2007, 10:23 PM

There have been a few posts lately from different people on charging issues.

I have been having problems myself. See the post "Dead Battery - where to start?" Which is still active now, just a few threads down. I know next to nothing about the charging system, so I may have asked some of the dumb questions for you already.

bigblue · #12 12-29-2007, 05:52 PM

Just to recap on this old thread, it was due to the fact that the instrumental cluster was disconnected. It's still off here and there due to other dash/interior/wiring issues but that was definitely why the system was not charging.

Bad engineer! No wienersnitchel for you tonight.

mcguiver7 · #13 12-29-2007, 08:07 PM

i'm in the same boat here. my battery keeps draining down and i'm only showing 12v at the battery so i removed the alternator and had it load tested at autozone and it passed. which light is the idiot light?

bigblue · #14 12-29-2007, 08:25 PM

Quote:

Originally Posted by mcguiver7

i'm in the same boat here. my battery keeps draining down and i'm only showing 12v at the battery so i removed the alternator and had it load tested at autozone and it passed. which light is the idiot light?

That doesn't necessarily mean that you have the same problem I did. I believe a bad fusible link or ground could also cause a charging problem even with a good alternator but lets assume it is the same.

It's the light that look like a battery. Easy to diagnose this one.

Do you have an instrument cluster attached?
Does the light come on when you first turn the key?
If not, the bulb inside could be out/gone and is likely the problem
If it does, does it go out after the engine is started?
If not, why haven't you noticed

mcguiver7 · #15 12-29-2007, 08:32 PM

yes the cluster is attached and the grounds are good. i did a 4spd swap a few weeks back and all grounds were cleaned. the problem was apparent before then as well. i don't recall the light being on while driving so there could be a chance it does not come on at all. kinda funny how the charging system is reliant on this little dash light.