'87 300e right tail light blows fuse every time
 

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.

perhaps if i reply to my own thread...
 

...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

Same mystery problem
 

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?

ha. now we have two threads
 

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
 

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?

fuses
 

before this had you attempted to modify the wiring at all? we had a car like this come into our shop with the similar issue, the customer had tried to install a trailer light for a tow trailer, he shorted something and damaged the bulb control relay, replacing the bulb control relay fixed the problem

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

Hi,
I also have the exact same problem with the #3 fuse shorting out. I have disconnected the tail light, headlight wipers, front right bulb, license plate lights, inspected all visible wiring and still the fuse blows when I turn on the parking lights. I have just installed a new radio/cd player which works fine - do you think I may have disturbed something in the radio cavity area? Also can you please tell me where the bulb control relay is located.
Spending countless hours and going crazy in the heat,
Tino

You might check the cigarette lighter wiring at the lighter/ashtray. Mine would short out and take out a fuse and/or tail light bulb, or leave a bulb on or not working. The wiring insulation stretched loose (exposing a small section of wire) when I pulled the radio, and would short when the ash tray assembly was bolted back in place.

this cigarette lighter causing a short sounds intriguing, because i have disconnected the wires from the lighter to run aux wires from the stereo through the hole where the cigarette lighter once was, and i only capped them off with electrical tape. now, if this is causing a short back there, would this indeed fry the bulb control relay? where is this relay and how much does it cost to replace? how can i tell if this is my culprit or does one simply guess and check at these things? this is not the same as the light control unit located under the fusebox cover, which i pray to the mercedes deities is not the problem..

What does the light control unit look like? Is it in back of the fuse box with the other relays?

The lighter is not on the same #3 circuit so how can it cause this problem?

Isn't the ashtray light on the same circuit as the instrument cluster though? It's easy enough to look.