this just started about a week and a half ago. first the fuse that controls the left front and rear right windows blew (fuse #8 i think). with that fixed, later that day the right tail light and the backlight to the instrument cluster went out. i replaced the fuse (#3, the circuit also has the cruise control, tachometer, and probably some others i'm forgetting) and it blew again. i am without a multi-meter, though i suspect i'll be buying one very soon having spent six months with this car now without one. i understand the longer of the boxes mounted under the fusebox cover is the one that controls the lights; the questions i have are relating to getting at the thing and testing it, cleaning it and possibly repairing or replacing it. i am still quite a novice at this type of thing.. does the part pull right out or is it more delicate than that? is there a way to test the unit? what method should be used to open and clean the part? also, i have never soldered anything in my life, so i wonder what advice anyone might have as to whether i should even bother trying to resolder connections as i have often heard here is a good way to fix these old components as they break down. if so, any advice before taking the plunge and buying a soldering kit (and a multi-meter while i'm at it)..? any advice would be greatly appreciated.

...someone might respond? please? i just know i would rather not replace this silly thing, and someone out there must have seen this before.

There aren't any silver bullets. You need, as a minimum, the owner's manual, a multimeter, and some test lead extensions are always handy.

Then you start looking for shorts. Go to http://mb.braingears.com, download the electrical troubleshooting manual and schematics, so you can print out the schematics you need for the suspect circuits.

Your car is 18 years old. Who knows what it's been through. I just spent several hours over the last few days trying to figure out why my backup lights didn't work (results in a nearby thread).

Electrical troubleshooting can be a massive amount of grunt work, and even if you are experienced, bizzare results can sometimes take you down blind alleys.

Duke

WOW Thanks for the manual...I had bought this 2 cd set on ebay for $10...but its GREAT to have on my computer..

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1993 Lexus SC300
1987 Mercedes 300E ..totaled out..
1991 Saab 900Convertible ..gave away..

I have the exact same problem with fuse #3 that controls the tail lights, instrument lights and head light washer units. When I plug in a new fuse it instantly blows when I turn on the lights. I tried to find the short by unpluging both tail lights and the wiper motors but the fuse still blows. If you solve your problem please let me know. Ohh on my instrument cluster the replace lightbulb warning is also on when I turn on the headlamps - is this also in your case?

yes, when the headlights are on the bulb indicator goes on. i'm going to buy a multi-meter today and start following the trail of wires wherever it leads me.. hope it's not the control unit. faulty wires i can handle, fancy electronic boxes are as yet over my head.

water in the rear light may cause that..

i lied about buying a voltmeter today. instead i disconnected each of these items individuall, each of them running on circuit number 3: the right taillight assembly: fuse blew; the right front parking light: fuse blew; the lisence plate lights: fuse blew. i'm out of fuses. unless it's something obscure (or something in the wiring i missed) i believe the short exists somewhere behind the instrument cluster. i'm sure someone here has taken this apart before.... any ideas? am i on the right track?

Fuse #3 problem solved.(BUT brown/blue wire -was does it do?)
After countless hours of not finding the # 3 circuit short (but I at least I am now more familiar with my car) I decided to unwrap and check all my new radio connections - and there it was - I had mistakenly joined what I thought was a ground which looked like a brown wire but was in fact a brown striped wire. I cut this wire and NO MORE SHORT.
I now have a mystery wire which is BROWN with a BLUE stripe - this wire went to the centre 5-pin plug at the rear of the old Becker radio. Has it anything to d with the alarm system - what should I do with it???
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1986 300E

i'm going to check that immediately, because i grounded that wire on the advice of a previous post on the stereo forum on this site...

well, that didn't work either. next i'm going to have to start ripping apart the interior looking for shorts behind the control elements and instrument cluster. anyone know why that brown and blue striped wire could have caused tino's short? is it possible i fried a relay by wiring it that way for all of this time? the saga continues...

Make certain that you carefuly check your work - some wires are brown with a stripe and at first glance they can be mistaken for ground.

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1986 300E

i finally found the short. after much trial and error i realized i hadn't checked the headlamp wiper unit. disconnected and all is well. i've changed all fuses and it was a good call, many were corroded at the connectors to the point where they came apart in my hands. persistence pays off again..

Wow, I'm have this exact same problem with curcuit #2 on my '92 (it has the headlamp wipers). I just bought a bucket of 8a fuses. I'll try those first. I've already started to look at he wires on the trunk lid but have not cut open the harnes and extracted them from the trunk to verify there is no short.

I thought I had a good test by checking resistance with an ohm meter from the body side of the fuse to ground, but the curicts the work normally, have the same nearly zero reistance... :p

So.. I'll try to locate the plugs for the wiper units to see if I can unplug them, pop in a new fuse and pray my lights come on. Just bought it, and neglected to verify the dashlights worked (dumb*** me - slapping forehead). She runs great though. My '90 with nearly twice the milage has never had these sort of issues. At least there does not seem to be any common circuits to the engine wiring harness which it sounds like the '91-'95 model years have issues with.

At least I can fully enjoy the car during the daytime still!!!!

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