Mharlos1

Hey guys, new to this particular site, as I wanted to broaden my internet scope to hopefully help me with an issue, so if I have broken any forum rules please let me know!

I will give a TLDR as well as a full recap to my knowledge for all required info on this issue.

TLDR;
Battery (new or old) won't charge while running because the alternator (new or old, yes I have a new and an old one for both battery and alternator to try and eliminate factors) isn't charging it.
Wiring seems fine, alternator tested, battery tested voltage on batt at start is 12.94, while running sits at 11.7 and lowers with higher rpm.

Full recap;
It started while driving home about 4 weeks ago where I had a dash camera plugged in, heater fan on, high beams on (mountain roads in the dark) and charging my phone (through dash cam port) all with a 115A alternator.

​​​​​​Noticed my high beams were going dim, then my SRS cluster light came on, then my airbag light, figuring it was a power loss I tried the wipers and they went REALLY slow. Thankfully I made it the last 10km in the pitch black with normal headlights and heater/dashcam/charger all off and the car died the second I put it in park.

I then charged the battery with a smart charger and it would hold 12.9V and would start once or twice, but wouldn't charge after that while running.

Those were the symptoms, here were the tests I did;

• Got new battery, same issue
• Fully charged battery, started car and pulled positive terminal off battery, car died (thinking bad alternator)
• Replaced alternator and repeated second test, same thing and voltage while positive terminal connected read 11.7V while running and lowering
• Ran multimeter in series with negative terminal to see if parasitic draw affected anything and only found 16.2mA draw (should be fine)
• Tested continuity on the D+ and B+ wires coming from alternator to power distributor (see photos for new ones, also not sure if it's called the power distributor) and continuity was there
• Replaced those wires anyway with new ones (again see photos)
• Checked the battery bulb in the instrument cluster to see if it turned on when key was on, it didn't..
• Removed instrument cluster but found the bulb+socket both had continuity and the bulb wasn't burned out

Is there a way to check continuity on the power distributor to see if the excitation wires work? Or more accurately, where on the instrument cluster plugins do I check for continuity , as I'm not sure who to fully read wiring schematics (see photos for instrument cluster)

I also heard it may be some battery regulator fuse box (not sure on name) under passenger seat carpet, and the fuses inside that but have not checked them yet. The reason I have not checked this yet, is because I would have to reassemble the instrument cluster, in order to see if the car works /starts to properly run the test for said fuse box. And I don't want to reassemble the instrument cluster until I know if there's a way I can check continuity on those excitation wires.

Am I missing anything? Does anyone out there have any sort of information that can help me? I'm coming to the end of my ropes, but I really don't want to sell this thing as I currently live out of it, and I have no other place to put my stuff.

If it helps, I have a 1993 190e 2.3L 8 valve.

Thanks to anyone out there with any information that may help me, and again forgive any ignorance I may have shown in this post 🙏🏼

jimyj

It sounds like there could be multiple factors contributing to your battery not charging while the engine is running. Even though you've replaced both the alternator and the battery, the issue might lie in the wiring harness or the connections between the alternator and the battery. Corrosion or loose connections can impede the proper flow of electricity, leading to insufficient charging. Additionally, the voltage regulator, which is often integrated into the alternator in modern vehicles, might be malfunctioning. If the regulator isn't correctly managing the output from the alternator, it could prevent the battery from receiving the necessary charge. Another possibility is a faulty ground connection, which can disrupt the electrical system's overall performance and affect the charging process. Given that you've already checked continuity and replaced the wires, it's also worth considering if there's an issue with the instrument cluster sending incorrect signals to the alternator, especially since the battery warning light isn't illuminating as expected. You should probably run a full system scan. There should be fault codes on at least one or more control modules related to this. You'll either need to take it to a mechanic, but if you want to figure this out yourself, then you'll need to get a full system scanner. The youcanic full system scanner is very good at diagnosing all systems, and there are other scan tools that can do this. Just be careful to use a full system scanner or you may scan the car and see no fault codes as some scanners can read all vehicle systems. youcanic can run an in-depth all system scan as well as diagnostics. I hope this helps, and feel free to reach out if you have more questions!

Mharlos1

Will this code scanner work on a 1993 190e? I have a small code reader I build (simple button and light) that flashes based on codes and tells you what code errors it got pretty accurately, will this work?

Also thanks for the information regarding the wiring, I may take off all connections associated with the alternator battery and replace them, or at least clean them very well.

As for the voltage regulator, I know it's possible to receive a new part that is faulty but I did run these tests with an old alternator as well as a new one I bought and got the same issue both times.. so I'm doubtful I had that bad of luck.

dolucasi

I know people do this but replacing an 80A alternator with a >100A alternator that is not made for the W201 started all the trouble here.
Sounds like a grounding issue to me since the warning light needs a ground connection. The hot end of that bulb goes thru a fuse in the fuse box to the cluster.
The ground side of the bulb is connected to the alternator again thru the fuse box with no fuse on that path.

From the instrument cluster the diagram I have shows some sort of a connector buss probably under or inside the fuse box. I suspect that buss/terminal connector maybe fried or corroded.
On my simple hanes manual it appears to be a connector that has an earth ground connection + 15 more terminals. So a 16 pin connector.
Instead of ripping up the fuse box which is a nasty job, you can ohm out all the wires from the cluster (6 wires) to their destinations (7 wires) one at a time to make sure you can near zero ohms.

I would start with the battery charging warning light which is a blue wire that goes thru this connector straight to the alternator again in blue.
This signal needs a path to ground thru the alternator. Seems like you are not getting that. While running the voltage on the blue wire at the alternator should be zero volts.

Not your typical failure mode in these cars but maybe the oversized alternator not made for the W201 contributed to the demise.

My 2 cents on this is to try and reduce consumption instead of oversizing alternators if you have more demanding electronics added in. For example nearly all bulbs can be replaced by LED bulbs that would save a lot of current drain on the battery.

Mharlos1

So.. feel like an idiot for not having seen this before.. but it looks like one of the diodes in the alternator is burnt out!! (See photos).So plan on getting another new alternator, but my question is, the new one got, why did it have the same issues? Maybe this is related but explain why I don't have the "new" alternator anymore; -It didn't quite fit into the housing properly so could get the bottom bolt in and the top one in, or vice versa but not both bolts completely in. The reason why wasn't too worried about it, is because wanted to see if when it was hooked up would it still work, whether it fit properly or not. Now hearing that it grounds through the body of the alternator into the engine. Maybe that explains why the new one wouldn't charge either?



This is the cover that sits over the back of the alternator, and right where it's burnt is right over top of the screw in the first photo.

190Efan

I think your problem might be a combination of things. The first problem is likely your use of an aftermarket alternator that your car wasn't designed to work with. In addition, you've added a number of electronics that your car's electrical system wasn't designed to be able to accommodate which is creating an additional electrical draw on your car's electrical system. W201s can get very crabby when they're having to work with an alternator they were never designed to work with as well as having to accommodate additional electronics that the car's electrical system was never designed to have to cope with. This is likely what's happened with your car. You've overloaded your electrical system in 2 ways, first by using an alternator that's too big and powerful and second by asking your car's electrical system to run additional electronics that it was never designed for. Go back to an OEM alternator and take out the additional electronics you've added and that should solve the problem.