Dear Dirk
If done right, a new wire harness is in general better than the original. I agree in that.
But …. As many vendors try to save money in many areas, it is difficult that price oriented reproductions match the quality of your original harness in many aspects as:
1. Many repro harnesses do not have soldered terminals at the fuse box, just crimped. Original harness was crimped and soldered
2. Many repro harness that have passed through my hands do not match the original cable coding colour scheme. I mean they just use plain color cables with no colour stripes. Mercedes used originally up to three colors on a wire so that you can know it’s service without tracking it down to all its extend.
If your wires are full copper, as it is in most of the lines of the ORIGINAL MERCEDES HARNESS, and the external insulation is ok you can keep them for another 40 years. They do not degrade so fast.
Of course that main wires as T30 circuits which are always energized, with no fuse protection, these ones should be replaced; first because there is no protection against a short, I mean no fuse on those segments, and also because these particular lines, even when they are full copper, they used a thermo resistant external cotton/resin insulation that does not withstand 50 years. They are always in bad shape once you expose the cables.
Same story with T50 starter selenoid signaling cable. It may look nice, but that one suffers from softened external cable insulation, which means that any pull of the cable will broke the insulation. Also, that one suffers from internal corrosion (more resistance for signals passing through), I presume because it’s made of a different alloy than full copper.
So in the case of MB pagodas even with a car not presenting any troubles, if the harness is still ORIGINAL, have always present on your mind that those lines can not be Ok. It’s just a matter of time that the catastrophic event will come. I mean a fire…. Compromised insulation on always energized lines without any fuse protection will sooner or later come to that end. First symptoms are batteries that drain faster than normal.
On the other hand, for non heat exposed original cables, like the ones that service headlights, horn, etc, those tend to resist the pass of time without major deterioration.
On headlights the problem which shows more often, is that they could be melted somewhere if any of the previous owners of the car installed 100 watt bulbs on the H4 socket. That problem is only evident when you strip out all the external branches pvc jackets. On a refurbishing job if that is the condition, lines are replaced for new ones.
The same treatment is applied for critical ground lines which are on the engine compartment, they are always replaced for new ones.
The part of the main harness that is inside the cabin tends to show no important damages except the ones that could be caused by running circuits with bypassed fuses.
All that is deeply investigated and any damage is solved by replacing lines with new ones with color coding and gauge matching with original wiring diagrams.
On Mercedes’ w108 story is different. I have seen many harnesses with internally corroded lines, I think that alloy used on signaling cables or for low wattage accessories is something different. Any line in section 1 mm2 or 0.75 mm2 tends to have this kind of problems.
Examples are:
1. Brake light lines
2. Brake fluid lines
3. Reverse light lines
Etc.
Best regards
L.Peterssen
