Okay, to start off, I'm not being a typical newb. I searched the forums for answers but can't find anything.

My problem is very odd. To start off, the car is a 1991 300E. When I bought it, I knew some things weren't working right but the price was right and I needed a car so I took it anyway because most of the things were working. Well now, I have some downtime. I am trying to trouble shoot the problem so I started with the fuses. When I opened the fuse box, the guy had some weird connection happening. Fuse 1 and 9 were connected via a wire. I disconnected it and replaced Fuse 1 because it was blown. I also replaced fuse C because it was blown.

Anyhow, at first only fuse C blew.

Before I go on, here are the descriptions:
Fuse 1 (16A): cigar lighter, switch heatable rear window, glove compartment light, rear wipe/wash system, folding head restraints/rear compartment, radio (ortho. back rest)

Fuse 9 (8A): diagnostic term. 6, hazard warning system, clock, front roof light, radio, vanity mirror light, relay comfort circuitry term. 86

Fuse C (16A): rear roof light, trunk light, rear door locking system, safety belt handover arm, seat back arrester, central locking system, door lights, reading lamps, aut. antenna, control unit seat adjustment

Fuse 1 and 9 were fine for a while. Fuse C blew instantly, twice. So I used a 25A fuse instead and it was fine for a little less than a day, then it blew along with fuse 1. As i took C out, I accidentally touched it to fuse 9 and that blew. So I disconnected the battery, replaced all three, reconnected the battery, and the 25A fuse in C lit turned bright red and lit on fire instantly, melting the plastic. Fuse 1 and 9 were otherwise fine. I disconnected the battery, left fuse C out and reconnected the battery. Now fuse 1 blew. I am extremely confused because for a while, everything was working despite the weird hookup.

Can anyone help or is it completely FUBAR?

omg. that sucks. i'm sorry...

& also have zero input on this topic...

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Matthew McIvor

2016 E350 4Matic Black/Black
2007 GL450 4Matic with Off-Road Pkg Silver/Black
1995 E300 Diesel White/Gray
1994 S600 Euro Black/ Black Velour
1986 560SL Blue/Blue/Gray
1986 190E Blue/Blue 93k

Haha, well you didn't help any but you did make me chuckle.

I know the later wiring harnesses on some W124s were very prone to failure from engine bay heat, the rubber would literally biodegrade. Check to see if the plastic sheathing looks look bad. Electrical problems are always a mess, do you have access to wiring diagrams? Let me know and I'll try to send some your way.

bavalova, apparently you have one or more shorts to ground in the wiring. Inspect for faulty insulation in the wiring and/or loose connections to the accessories on each particular circuit. Never install a higher amperage fuse in a circuit than the fuse chart specifies. That no-no may have overloaded the wiring and caused additional problems. Based on your description of the electrical problems with your 1991 300E I wouldn't suspect that the engine wiring harness is the cause. A faulty engine wiring harness would cause the engine to run erratically. You may want to consider having a MB-trained tech diagnose your electrical problems before you complicate the situation further.

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Fred Hoelzle

Ditto, to the overamperage fuse. You may have melted your problem right into another circuit now.

If playing with fuses is the height of your technical competance here, you might consider professional help.

Your car would not be one of teh ones that had harness problems on the motor.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I think you guys are right. Some more of my fuses busted. I have to check exactly which ones. I may just take it in to have it checked out. Dang it all.

Appatula, a wiring diagram might help. At least I can take a look if nothing else. I'm sure taking it to a shop would be pretty costly.

have same problem with fuse c 93 300e. did you check module under rear seat ? replaced mine but problem returned in 3wks

Its been awhile since the original poster posted results... I wonder what ever became of those electrical issues?

Ditto that again... NEVER install a higher amp fuse for a circuit that calls for a smaller fuse... that is a recipe for disasters!

The wires running to the trunk lid have come apart on more than one occasion in my cars. It's on the left trunk lid hinge. The trunk light switch is in the lid.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

The 1990-94 Lexus LS400's were bad for this as well. The wiring loom in the trunk is connected to the trunk hinge and over time the wiring will become twisted and frazzled and the wiring will fray and cause an array of electrical weirdness. No fires have ever been reported with it, but it does cause very strange things like warning lights on the dash illuminate for no reason, the transmissions electronics go haywire, etc, etc. The fix is easy.... simply cut away the tape from that area and splice/tape up the frazzled wiring and its fine. Seems as if the original wiring loom was too tight originally causing this problem, which is odd, because Toyotas of that era (80s-90s) are generally well-known for their excellent electrical systems.

Here is the loom in the trunk of my LS400 that has already been addressed... poorly, but it has been redone and all is fine now, but you get the general idea...