Garage > Mechanicals

Inherited wire mess 1979 300sd


Hi all I inherited this 79 300sd that needs a little work. I'm pretty good at following diagrams but I'm a little confused at what I'm looking at. Obviously non factory wiring, I debulked most of the wiring that wasn't installed correctly anyway to start with a clean slate. It appears there are two harnesses. I assume the ones with rings would be from a fused panel to the appropriate switch ect and the other complet harness is power out. Any help would be appreciated.

Looks like you need this:  The seller has wires attached so it should be easy to redo it cause you can see color codes.  The box also has a top that you can find on eBay.  Finally, there's a relay plate in the fusebox towards the front that relay sockets snap into.  You'll want to find one of those along with a bunch of relay sockets.  I'm not sure where to get those, but somebody must have them.   My comments are for W116's in general, somebody else will need to help with details for the 300SD.  Good luck and cheers,

Here you will find a wiring diagram.

Someone may have one specific for your model.

Most of what I see in your photo is stock wires with some obvious newer splices.

This box on fleabay has the relay brackets mentioned.

The wires with rings contain both the power source and destination wires. Your job will be to sort them out.  :o

How unfortunate that someone left you with this mess to repair.  Get new copper fuses. Before you try and assemble make sure that you dont have a water leak below the box.  Now is a good time to repair that! The lower corner rusts and allow water into the cabin area. Spray water in there and see where it goes. Look under the drivers carpet area.

I've managed to get most of the major circuits figured out just need to clean up the mess and wire to the fuse panel. I am curious if this switch assembly is missing a wire or not and if anyone knows of the top of their head what it is. I looked at the diagram and I'm not sure.

This schematic is specific to a 300SD.  The schematic literally tells you everything you need to know.  Circuit numbers, wire colors, and where the wires go.  Don't forget that U.S. cars do not have a rear fog light, so the wires for that will be missing. 


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