dougcabot

My car: 1993 300CE Cabriolet. My problem: battery drain. My mechanic (MB specialist) isolated the draw to fuses 9 and C, and worked on it for a few hours, and called me to say I could come get my car because he can't figure out the problem.
Any suggestions? Anybody know a mechanic savant in the Boston area? (I'm in Salem.)

fabbrisd1

You can do some research and give your mechanic a short list of issues to check: a whole bunch of sh*t runs thru Fuse 9 - examples to check in the fused systems are : failed interior door light switch - trunk light staying on - rear cabin light switch - failing convenience module - security system - there is no magic bullet - a meter and patience to go thru each circuit 1x1:

See CFM thread: https://www.benzworld.org/forums/w12...rent-leak.html

https://www.benzworld.org/forums/w12...fuses-9-a.html

dougcabot

Thank you.
He mentioned is that he doesn't have the wiring diagram for the cabriolet version.
If anyone else is having a similar issue maybe this will help. I sent it to him...
http://www.w124-zone.com/downloads/M...rbleShting.htm

BenzosNoLorenzo

Sometimes getting diagrams is a bit more of a pain then actually following and tracing the wire itself. 9 and C there is a ton of components that run through there. Multimeter and patience goes a long way. Also my rule of thumb did you clean your grounds and check them? Also Mercedes-Benz source.com they have pretty good troubleshooting videos sometimes you have to pay sometimes you don't but they're always worth it I've had a lot of problem solved using that website

Realkonceptz

I will concur with Benzoz on MercedesSource .com. Ken knows these early to mid 90's Mercedes Benz cars inside and out. You can catch a lot of his videos on Youtube and if you need more indepth videos he just charges a few few buck for his video walk-throughs. I actually have watched everything he has done on the W124 body before I bought mine. Very informative and accurate.

Jack McCarty

You’re aware that these cars have major wiring issues? The wiring harnesses were designed to biodegrade over time which has to be the worst “green” decision MB has ever made. The wiring harness has to be replaced before proceeding with further wiring work.
just FYI.

Realkonceptz

I agree with jack, I remember the 91-96 Mercedes vehicles having a big problem with the harnesses degrading to quickly and having to be replaced with ones that were not designed to be bio degradable. Ken from Mercedes Source actually has a video up on YouTube that talks about this issue in detail.Here's the link:

Jack McCarty

Actually, there are distinct differences in the final 93 300CE & 94-95 E320 vehicles vs.
the first gen 88-89 CE’s & the revised 90-92
CE’s:
for the 3rd gen 93-95, MB made a costly mistake in making the Wiring Harnesses
bio-degradable in a profoundly perplexing
effort to “go Green.”
if your vehicle is the 93-95 gen, the first decision has to be replacing the WH.

Realkonceptz

It's not a question of "if" Jack, the vehicle he is referring to is a 1993 300CE as he mentioned in the beginning of this thread. Basically what we are trying to say Doug is that more than likely you will most likely need to replace the wiring harness with the the updated harness for your year and model. there are several online vendors that carry these harnesses such as Partsgeek.com and Pelican parts.com. They can range between $1200-1500.

Floobydust

I agree about all the issues with the ecco junk wiring - the engine harnesses should be replaced if it has not already been done. If there is a Delphi label on the harness by the battery, it is a new replacement harness.

BUT, current drain on Fuses 9 and C has nothing to do with the problematic engine wiring harness. Check the following known areas for this type of current drain:

Make sure the fuse contacts are free of corrosion - since fuse C and 9 are hot all of the time they tend to undergo galvanic corrosion. Current draw will go up unless both circuits are properly energized.
Anti theft alarm module in the passenger foot well - check by disconnecting (common issue)
Convenience Control Unit under the left rear seat - check by disconnecting (common issue)
Power door lock pump under the right rear seat - check by disconnecting
Radio "memory" hold circuit - check by disconnecting
Trunk light staying on - throw your phone on video into the trunk and verify that the trunk light goes off when the trunk is shut.

Also, this link may help with the schematic: http://www.autolib.diakom.ru/CAR/Mer...NG%20DIAGRAMS/ It's for a '95, but the fuse C and 9 circuits should be same.
Good luck.