Wiring harness:

http://tinyurl.com/8nx7v

http://www.peachparts.com/Wikka/M104WireHarness

The MB E-class owner's bible suggests that shielding the affected wires with taped pieces of pliable plastic (e.g. from a factory coolant bottle) can be an effective repair. That seems worth trying if the insulation breakdown is limited, but I've seen photos of spectacular general degradation:

http://tinyurl.com/24m42n

Nevertheless, there's no sign of it yet in my 1996 Coupé, which is checked for this problem at every service.

One overlooked source of repeated problems with a head gasket is that some get done without skimming. My mechanic says that the heads all warp and he's never found one that didn't need it. Here's the article referred to in an earlier post:

http://www.continentalimports.com/ser_ic100345.html