fuse, roadmap to solution - PeachParts Mercedes-Benz Forum

janko · #1 05-21-2003, 07:21 AM

83 240d. having to replace the #8, i believe, fuse - the one that has the circuit that protects fuel and temperature guages, turnsignals, etc - on a regular basis. the question: how do i proceed, hopefully in some logical fashion, to find the short. sometimes i can drive all day and no problem. sometimes the fuse will blow after a few minutes. i have not been able to discern any correlation to what is happening in the car with the fuse's blowing. thank you.

jude · #2 05-21-2003, 09:48 AM

suggest you replace the fuse with a higher amp fuse. continue to do so until you melt the wire that is shorting. should then be easy to find the offending circuit."

P.E.Haiges · #3 05-21-2003, 10:21 AM

Janko,

I would suggest you not use Jude's method to find your short circuit. It could possibly cause a fire and solve you problem in a way you don't want. Fuses are in circuits to prevent wires from melting.

An intermittent problem like you have is very difficult to find. If you can disconnect one part of the circuit at a time to see if the blown fuse problem stops, that would my suggestion. I realize this is difficult in a car wiring because so many wires are wrapped in one cable and go thru one connector.

First thing you should have is a wiring diagram. They are in the MB repair manuals. I don't have one for your model car but someone here might be able to make a copy for you.

P E H

#4 05-21-2003, 04:31 PM

make sure you're replacing with 'slo-blo' fuses that don't blow with a short spike. a spike might blow an electronic component but won't cause a fire.

lrg · #5 05-21-2003, 05:40 PM

I agree with PEH. I'd suggest starting the process with your directionals. These pull a fair amount of power and are subject to the elements which can result in corrosion related faults. For starters I'd remove the bulbs at all four corners and carefully clean the contacts with fine sandpaper. If you find some corrosion then be sure to clean those especially well. While you are at it it wouldn't hurt to just replace any bulbs that look suspect (sorry PEH, I know they may still be usable.) This may not solve your problem but it's a good place to start.

P.E.Haiges · #6 05-21-2003, 06:41 PM

Irg,

I disagree that replacing the bulbs will help find what is blowing Janko's fuse. Corrosion in the bulb sockets may cause an open circuit and the bulb may not work, but it will not cause a short circuit which is what blows fuses. If the bulbs work, leave them alone, they are not the problem. I say again:If it ain't broke, don't fix it.

P E H

lrg · #7 05-21-2003, 06:49 PM

PEH,

You are correct. The corrosion won't cause a short but the moisture that caused the corrosion can. If you have a leaky lens the moisture tends to cling to the corrosion and can cause a short. It may well be that that is not Janko's problem but it is both easier to start there than at the gauges and also, in my opinion, a higher probability of being the faulty circuit, hense my recommendation that he start there.
LRG

fz500sel · #8 05-21-2003, 06:59 PM

If anything start at the bulbs CIRCUITS. The bulbs are the last thing on those circuits. You would be better off disconnecting the wiring going to those bulbs. Once again, you will need the wiring diagrams foremost. Then isolate via disconnecting one section at a time, i.e. turn signal circuit, then try fuel gauge circuit, etc.

It's not gonna' be easy but once you find it you will feel like you can conquer the world!

Good luck,
Frank