Need Electrical Guru!
 

1989 300E 120k M103 engine

No. 6 fuse blows intermittently without any pattern. Fuse is for horn, turn signals and outside temperature gauge. Inspected/cleaned all bulb holders, wiring, and fuse holder with no luck. Any ideas?

According to the FSM Fuse 6 Powers:

Turn Signal / Hazard Lamps
Outside Temperature Gauge
Warning System
Horns.

Perhaps you've got something shorting out randomly? Have you worked on anything recently? When did this start?

http://i.imgur.com/aICUil.jpg

Hi Again!
 

Did replace the ourside temperature display module last year. Cannot recall if it was before or after this problem started!

You say random without any pattern, but in general how long does the fuse last? Are you sure you are using the correct amp fuse?

Electrical Short
 

In general, a fuse may last for a few days but just went about 5 months without shorting. Just blew 3 fuses within a few minutes (8amp and 1 16amp I threw in there to see if that would hold). 8 amp is spec.

Maybe I better take a closer at the wiring around the trunk area to see if there is some hidden insulation problems............or even pull the cluster to check on the warning lights/wiring and the outside temperature module.

Keep trying a 16 amp fuse, and watch the wiring die.

You might pull the cluster and check out the plugs, etc, for the outside temp display. Something may be pinched.

I was thinking of the back of the cluster too, or see if anything has been added to a circuit, like a plug in for a radar detector, anything like that. These intermittent ones are always a joy.
If you are lucky you can mess with a few of these components and find the short. You could pull up the fuse box and look inside for signs of shorting too. I would suspect the problem lies between the fuse and a component, not after a component.

Fuse
 

Starting to see a trend!

Fuse blows with a minute or two after driving with the blower running. Fuse blows and blower slows down for about 5 seconds then resumes prior speed. I wonder .......Hmmm, the climate control system is fuse 7!

May I better look at the connections under the fuse holders to see if anything is arcing under there!

Divide & conquer!

Go to the bottom of the fuse box where all the wires connect to the fuse box & cut and
INSERT an in-line fuse holder into each of the wires. $5-10
USE fuses rated slightly lower than the one in the box. Then when something QUITS working you will find WHAT consumer is blowing the fuse. Good luck

Culprit?
 

A local Mercedes shop confirmed for a nominal fee that the climate control unit was going bad and somehow affected fuse #6 which was on an adjacent circuit. The fuse only blew up when the climate control was on! They substituted another climate control unit and everything was fine!

Guess I am in the market for a reconditioned climate control unit or someone who can fix mine! James Dean?

That "divide and conquer" stuff don't go over too good here in WI.

I have a climate control push button unit out of my 1987 300e available. My original one went bad and I replaced it. The car was totaled last month by a careless driver, so before the insurance company picked it up I put the old bad one back in and kept the working one. It only takes about 10 minutes to swap it out. I want $50 for it.

Pete

CC Unit
 

Thanks for the offer!

I decided to buy a remanufactured CC unit at a discount with a warranty. Hope that was the issue!

hey big dog,

I'm a bit late to this thread. I've done some re-work on some first gen 126 climate control units. But never one of the newer style ones. If you've no use for the old one I'd love to give it a shot. See what was going on in there..

Have to send my old CC unit back to the seller for a core refund. Would have been awesome to have you repair my cruise control amp and CC unit!