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  #1  
Old 09-22-2010, 10:28 PM
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Join Date: Jul 2008
Location: Kernersville, North Carolina
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87 300D Fuse Follies

Apologies in advance if there are already posts on this topic, but I'm a single dad and just don't have time to research.

Anyway, fuse "C" constantly blows. It controls the door locks, power antennae, rear courtesy lights, dome light, trunk light, etc. It started blowing several months ago. When I replaced the fuse, everything worked fine, and I could go a week or so before I had to replace it again. Lately if I put a new fuse in and drive to the store, it will be blown by the time I get there.

It uses the red, 16 amp fuses. One time I ran out of reds, and the fuse had blown after the doors had been locked. I could open the doors manually, but I needed fuel, so I put a blue 25 amp in the C slot temporarily, so that I could unlock the fuel cover. I forgot about it, and it, too, blew, melting the fuse and leaving burned marks on the paper fuse diagram attached to the plastic fuse bank cover.

So something is shorting out somewhere and it has gotten progressively worse. Sometimes it blows after I lock the doors; sometimes it blows while driving. But I've never been able to "make" it blow by using the items it powers.

Has this happened to anyone else?
Thanks.

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  #2  
Old 09-22-2010, 10:33 PM
vstech's Avatar
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Location: Mount Holly, NC
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wiring paths will have to be traced until you find the problem. harnesses go through channels under door sills, and so on.
perhaps others with similar problems will post their solutions.
I have same car, with several missing fuses, and windows that don't work, so odds are good I will be doing the same tracing you are facing... post pics, and I'll do the same if I find something.
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  #3  
Old 09-22-2010, 10:43 PM
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Quote:
Originally Posted by Merce-Me View Post
Apologies in advance if there are already posts on this topic, but I'm a single dad and just don't have time to research.

Anyway, fuse "C" constantly blows. It controls the door locks, power antennae, rear courtesy lights, dome light, trunk light, etc. It started blowing several months ago. When I replaced the fuse, everything worked fine, and I could go a week or so before I had to replace it again. Lately if I put a new fuse in and drive to the store, it will be blown by the time I get there.

It uses the red, 16 amp fuses. One time I ran out of reds, and the fuse had blown after the doors had been locked. I could open the doors manually, but I needed fuel, so I put a blue 25 amp in the C slot temporarily, so that I could unlock the fuel cover. I forgot about it, and it, too, blew, melting the fuse and leaving burned marks on the paper fuse diagram attached to the plastic fuse bank cover.

So something is shorting out somewhere and it has gotten progressively worse. Sometimes it blows after I lock the doors; sometimes it blows while driving. But I've never been able to "make" it blow by using the items it powers.

Has this happened to anyone else?
Thanks.
Check the wiring for the trunk light, that wiring passes from the chassis through the tubular hood hinge on the driver's side of the car, this wire is prone to wearing through where it passes over the sharp edge. There is some protective sheathing over the wiring at that point so you'll have to give it a close inspection. That wire is always "hot".
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  #4  
Old 09-23-2010, 12:36 PM
Livin' on the Edge . . .
 
Join Date: Jul 2008
Location: Kernersville, North Carolina
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Quote:
Originally Posted by Billybob View Post
Check the wiring for the trunk light, that wiring passes from the chassis through the tubular hood hinge on the driver's side of the car, this wire is prone to wearing through where it passes over the sharp edge. There is some protective sheathing over the wiring at that point so you'll have to give it a close inspection. That wire is always "hot".
Thanks! I'll check it out and let you know...
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  #5  
Old 02-15-2011, 03:19 PM
Livin' on the Edge . . .
 
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Location: Kernersville, North Carolina
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Thanks for everyone's help! After checking all the wires and connections I could find, I still couldn't find the problem, and I pretty much just gave up.

But then, thanks to the guidance of this forum family, I ventured into the process of reattaching the armrest on the driver's side door panel. When I pulled the panel off, I noticed that there was a lot of loose change caught between the panel and the door frame, and that a quarter was lodged between door frame and the curb light assembly. When I removed the quarter I noticed telltale burn marks on it! I haven't popped the fuse since!

However, now I have a new query... While removing the quarter, I saw a spark and heard a pop (guess I should have disconnected the battery first) and the bulb went dark. I figured that I blew the bulb, so I replaced it. But it still didn't work with a new bulb, so I figured I must have damaged the bulb assembly (which is a small price to pay for solving the bigger problem).

But now I've noticed that when the passenger door opens, the light comes on as well as the passenger curb light. But when the driver door opens the passenger light doesn't come one. I've checked the switch with an ohm meter, and it works fine. Any thoughts?
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  #6  
Old 02-15-2011, 04:01 PM
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Location: Outer Banks, NC
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Not sure about this, but if the door-vacuum pump is on this circuit it may be over drawing current to produce the vacuum. It's located under the back seat. Might be worth a look if it is indeed on this electrical circuit. Don't ask me how I know...
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  #7  
Old 02-15-2011, 07:36 PM
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The interior light circuit is complicated; I had a real adventure getting my '87 fixed. A few points:

• Mercedes used stranded wire that was too coarse; in places where it gets bent back and forth a lot, such as between the A and B pillars and the doors, they can break. This affects both the power windows and the interior lights. The trunk light wiring is at similar risk.
• The front dome light and puddle lamps are powered through a relay that controls the left-key-in-ignition buzzer circuit. The front dome light and front puddle lamps go on together with either front door.
• The rear dome light and rear puddle lamps come on together when either rear door is opened.

This is how it's supposed to work. There are unfortunately many ways in which the wiring can fail.

Jeremy

• The trunk (or rear cargo area in T-sedans) is on the same fuse.

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