W123/300TD charging problems. Help! - PeachParts Mercedes-Benz Forum

Crackstar · #1 03-17-2008, 08:27 PM

Hi all!

I've been having problems with my battery/charging systems in my 1983 300TD wagon.

First I had a BAD battery, that was replaced. I got to drive around for about a week, then on my way to work I got a sketchy start, then when I wanted to leave work, nothing, zip, zero, nada. I have been reading lots of the other posts about similar situations, but they all seem to be on newer model Benz's. Now in 2001, the bearings went bad and stuck us in Ft Stockton Texas, we were lucky enough to find a place to re bearing and re brush the stock alt.

Since 2001 I have replaced three or four voltage regulators, usually when the VR goes bad I lose all my lights. I replaced the VR when I noticed my battery wasn't taking a charge, later I took the battery (one year old three year warranty Advance Auto Parts unit) and it tested good, but still wouldn't hold a charge, I replaced the VR again, thinking that the eggs smell I was getting in the cabin was the battery getting over charged. Plus I have a huge pile of scale in my battery tray from it puking. Finally about two months later, the battery tested bad, and was replaced.

Currently I get 11.2-11.3 volts at idle and nothing more with increased RPM's.

I'm trying to find out proper diagnosis techniques to rule out battery and alternator and VR, rather than continuing parts swapping. The three or four VR's I replaced were worn down and looked like they needed replacing, the last two I swapped out had very minimal wear and still look useable, one was Huco, the other was Hella.

Sorry if this post is long, I wanted to lay it all out as best I could, new battery(one week old) new VR(one month old) and the Alt was rebushed and brushed in 2001.

Any tips, thanks in advance

chuck

hangit · #2 03-17-2008, 08:32 PM

Take the car to your local Autozone or parts place of choice that can test the electrical system. Your battery should read 12.4 volts or so with engine off. At 2000 RPM you should have a reading of 13.5-14.5 Volts at the battery. Sounds like your alternator might be bad. I just went through the same thing with my 240D.

John

Crackstar · #3 03-17-2008, 08:48 PM

One of the things I was trying to avoid was dropping the Alt to get it tested, or just swapping a new one in. A friend with another 300TD sedan, had a similar problem, paid out the nose for a new alt from the Mercedes dealer and still had the same problem...When he asked me about it I immediatly thought VR, we swapped it out and still the same problem, a fully charged 1000cca battery would start the car for about a week and then leave it dead, not even take a charge after 30-40 minutes of driving 60+ 3000RPM

hangit · #4 03-17-2008, 09:14 PM

You don't need to drop the alternator to have AZ test it. They wheel their test cart out to your car and hook it up and run diagnostics. Check with them for a rebuilt unit, lifetime warranty.

Are your wires from the alternator to the starter in good shape, corrosion anywhere on connections? Battery connections corrosion free? Battery ground to frame ok? I'm not an expert, but I just went through the same thing and I know how frustrating electrical gremlins can be.

John

kerry · #5 03-17-2008, 09:19 PM

Why not just put a multimeter on the battery and monitor what is happening. Run some wires into the passenger compartment if necessary and monitor the voltage over a number of days to see what the system is providing to the battery.
That's after you replace either the voltage regulator or the alternator because with those voltages, you're not getting any charge to the battery. Do you have another voltage regulator you can swap in?

Crackstar · #6 03-17-2008, 09:26 PM

Hook it up to what? I took it to my local Advance, they wheeled out their test cart and hooked some cables to the batt terminals, and it only showed the 11.2-11.3 v at idle, with no increase in voltage at higher RPMs. Plus, when I got there I left it running in parking lot till one of the lackeys could wheel the cart out there, after seeing 11.2-11.3 I was told I'd have to bring them the alt so they could bench test it.

Battery terms are clean, cable ends are clean, there is noticable green stuff on the exposed part of the negitive cable going to the chassis, the chassis ground is clean, even put a new nut and bolt. All three wires from the alt plug are clean and intact and the female spade connectors are clean also. Wires are cheap I'll look into replacing them..

Crackstar · #7 03-17-2008, 09:30 PM

I'll try monitoring my volts, and stick in another VR, as for VR's, what maufacturer would you recommend, Huco, Hella, Bosch($$$)?

#8 03-17-2008, 09:30 PM

Quote:

Originally Posted by Crackstar

Wires are cheap I'll look into replacing them..

As an experiment, try running a jumper cable from the negative battery post to good ground points on the chassis and the engine block. If things improve, you will know you are dealing with a bad ground connection someplace. It's easier than replacing cables.

kerry · #9 03-17-2008, 09:31 PM

It's either your alternator or your voltage regulator. I don't see any options other than swapping in a new or known good regulator to see if it fixes it or taking off the alternator for testing and replacement.

yellowbenz · #10 03-17-2008, 10:48 PM

This doesn't help you but I've got the same problem. I went from a new battery to a new VR to a new alternator (original battery and alternator failed bench testing at az)

I've been thinking about opening up the insulation on the wires to check the output from the alternator. I'm hoping the wiring diagram from the manual helps me out here. It looks like there are three connections at the plug. Two output I guess? Is there an input to the alternator that "activates" the alternator? I dread taking off the alternator and having it bench tested. It fails the test that my portable battery charger runs. There is some corrosion at the plug. I wonder if I should just get another plug and replace the current one.

Would it be out in left field if I just spliced in a wire from one of the outputs and hard wired it to the battery post clamp? This is the direction I'm leaning towards. What about Cervan's idea of replacing with a one wire alternator?

Anybody have a good wiring harness for sale for a 1978 300D?

Crackstar · #11 03-18-2008, 07:10 AM

Could you E-mail me a copy of that wiring diagram?

Chuck@lumenlab.com

thanks

hangit · #12 03-18-2008, 09:07 AM

I ended up making my own wiring harness for the new alternator. Used 10Ga wire for the two large spade connectors. These go to the starter pole. The third 16-18Ga wire is for the battery indicator light on your dash. PO had really screwed up the wiring, so I replaced his inept work with new. Now charging at 14.5V! Not hard to do, just jack the car up as high as you can so you have plenty of arm and body room.

John

Crackstar · #13 03-18-2008, 09:34 AM

Hangit,
I traced the harness off the alt and it seems that the three wires folow all the way up the fender then into the firewall, somewheres behind the glove box. This is all stock wiring, the PO of my car didn't mess with anything. I cant seem to figure out how charge seemingly gets to the battery, the black cable goes to the chassis, the red is huge and disappears behind the engine and the firewall, I think I am surprising ignorant of my cars wiring set up. I may very well be missing something, but all I ever see attached to the alt is the three wire plug and the VR...I have another look at lunch and post back, this is a wagon and everything under the hood is in a much differnt place than a sedan

hangit · #14 03-18-2008, 10:10 AM

I emailed you the factory wiring diagram. All the wiring harness on my 240D are clearly visible in the engine bay. How many wires are connected to your starter? I think you should see 3, one from the battery and 2 from the alternator.

John

Crackstar · #15 03-18-2008, 12:16 PM

Indeed I have three wires on the back of the starter too. one big fat one to the + on the battery, the other two are connected to this wiring block on the fender. (see attached) Then other wires are connected to those that disappear into the cabin.
Doo Doo Camera phone pics i hope they come out ok...