I repalced the wiring harness on my 1995 SL500 (Similar Engine) after the dealer quoted me $1600 for the new harness. (No Labor) He assured me that it was made to the same specs as the origninal harness. There are many comments the subject on this and other forums, so I won't comment further and let you decide on the quality and merits of this particular Mercedes part.
I found the job quite easy. I used Belden 656702,18 AWG Style 1569 - Rated at 105 deg. C. This is a common oil and gas resistant CSA approved wire. (Slightly larger than orginal). Marine wire is a good alternative but get the UL or CSA specs on-line first. I reused all injectors and connectors by carefully soldering/heat shrinking to the new wire.
The key to the job is to get a schematic ( ALLDATA DIY ) and a good ohm-meter and spend an evening planning - marking and preparing. I did this on a Thursday night(3 Hrs) and did the job Friday night (5 Hrs). I cleared all the codes and went for a ride. I did this in early June. There are high temperature wraps available from places like McMaster Carr which I purchased but did not use. I went the summer watching the harness and measuring the wire temp. after long drives in 90 deg F plus heat. The wire never got above 70 deg. C. I will add the temp wrap next spring.
Easy job - under $30 - Engine runs great. E-Mail for Pics and more details.