Hello Mike,
I use sections of original wire from donor Mercedes sedans of the era to repair wires like this. In this way I am able to get the original size, color and configuration.
The sleeving can also be used. If a donor is not available, heat shrink tubing will substitute and a minimum of 14 gage stranded wire will work in a pinch.
Contact Rhode Island Wiring Harness to get exactly the correct new wire size and colors new. They reproduce many Mercedes wiring harnesses. They may sell you some correct wire and sleeving.
Joe Alexander
Blacklick, Ohio