Fuse #15 is blown, and blows instantly when replaced (with the proper 8 amp white fuse). So there is a dead short. I confirmed that the red (positive) wires leading away from fuse #15 are grounded out, in other words, in direct contact with the chassis (negative) somewhere.
Fuse #15 provides power to: the trunk light, the INterior lights, the door lights, the power antenna, and the "warning monitor term. 5". (BTW, what is the "warning monitor term. 5"?)
A Mercedes mechanic suggested that a short in the Power Antenna is typically the culprit when fuse #15 keeps blowing like this. But my power antenna checks out working properly; and even when the power antenna is completely disconnected from the car, the dead short in fuse #15 is still there.
So...I am stumped! Any prospective solution much appreciated.

Welcome to the forum.

Take a look at the left side bracket that supports the trunk lid. There are wires that run along the bracket and up to the light in the lid. The wires get flexed repeatedly when the lid is opened and they will finally fail at this location. I recently had to repair the ground wire to get the trunk light to function again. The supply wire was also in poor condition but not yet broken.

The same situation could also apply to the door lights..........a broken wire leading through the door jamb.

I have a "short" (ground fault) narrowed down to one specific wire. Can you tell me where the wire goes inside the car ('84 300sd, W126) after it leaves the fuse box (under the hood)?
One of the red wires that leaves fuse #15 is a single red wire with a number "15" label right on the wire itself. Of the 3 wire connections at fuse #15, only that single, specific wire, labeled #15, has a dead short. If you can tell me where that wire goes after it leaves the fuse box, I can find and fix the short!
I appreciate your consideration.

Do you have DSL/better internet access? If so, this on-line service manual may help.

http://mb.braingears.com

If no DSL, then I can take a look tomorrow to see what wire you are referring to. Sorry, my wiring diagram has no fuse numbers on it. Can you tell me what circuits you have listed on the fuse box cover for fuse #15?

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

There are two .75mm red wires coming off of fuse #15. One wire is for the courtesy lights and one is for the warning system.

I'll bet that you've got a short in the lines to one of the doors.

I used to have a 1985 300 SD. Wish I had kept it. Got great mileage. My blown fuse problem was solved when I pulled the two pin switches from the drivers side door column. One of the switches had worn out and caused the short.

__________________


Selling used Mercedes parts on Ebay...always changing...
cdplayer51 take a look!
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Thank you for your interest.
The fuse box cover says that Fuse #15 provides power to: the trunk light, the INterior lights, the door lights, the power antenna, and the "warning monitor term. 5". (BTW, what is the "warning monitor term. 5"?)
I have the following wires at fuse #15 with the following "symptoms":
1) One (1) red wire. It is never shorted.
2) Three (3) wires together: two (2) are red, and one (1) is red with white/yellow stripe. It is shorted when all the lights, etc. are connected as normal, but it is not shorted when all the lights, etc. are disconnected.
3) One (1) red wire with the #15 on it. It is always shorted.

Thank you for your interest.
As you suggest, I'll carefully look for a shorted red (+) wire in either 1) the trunk lid left side bracket or 2) a door jam.
To be clear, I have the following wires at fuse #15 with the following "symptoms":
1) One (1) red wire. It is never shorted.
2) Three (3) wires together: two (2) are red, and one (1) is red with white/yellow stripe. It is shorted when all the lights, etc. are connected as normal, but it is not shorted when all the lights, etc. are disconnected.
3) One (1) red wire (with the #15 on it). It is always shorted.

The chances of having two different circuits with shorts is pretty slim. What's the testing procedure that you're utilizing to verify a short? Confirming a short is not easy because many of the devices are grounded, specifically all bulbs on the circuit.