Dear friends
Some weeks ago, I finished an interesting project on which a custom wiring harness was built for a customer in Germany.
This guy bought an original W109 300SEL 6.3 which was terrible rotten at a point that he decided to buy another car with similar structure to pass all the 6.3 stuff to that body.
He sourced a nice perfect body 1972 W109-4.5.
At the beginning he thought he could transplant everything from one car to the other. When he faced the electrical part noticed that the 6.3 harness didn’t fit, specially on the cabin side as many accessories are on different places ….. , and therefore he contacted me.
He sent me to Venezuela both harnesses and wanted me to build the best of both.
Customer wanted to keep the AC system present on the 4.5 harness, so I decided to keep that harness as the base of the custom project.
As you all may know the 4.5 cars all were fuel injected with a Bosch D-jetronic system, with an ECU on the right engine bay fender, and a separated engine control harness which takes the reading for various combustion variables and do control the electric injectors.
Well all those systems and relay terminals had to be removed from the 4.5 harness.
On the other hand, basic things as the position of the alternator and ac compressor were opposite on the 6.3 compared to the 4.5
That made me to built from scratch all the charging system, and reposition the signals and relays that control the AC system.
The 6.3 has an array of relays to control the cold engine startup on the left fender close to the vacuum booster. All that was build from scratch NEW in order to have reliability. The shortcut will have to take those lines and elements from the old 6.3 harness, but I decided to take the long way, the quality way…..
A 6.3 harness has a 12 pin connector on the center of the firewall where the engine control harness is plugged in. That was build as well including some new signals that were not on the original design as is a line for the temperature sender.
The central instrument cluster branch and connector from the 4.5 was altered to fit the tachometer installed on a regular 6.3 central instrumentation, as well as a novelty which was to have an electrical signal driven temperature gauge. The customer bought an instrumentation circuit board coming from a late w114 sedan (1973 onwards) which came with that option.
The automatic transmission control on a 4.5 is totally different from a 6.3 so that part was build from scratch again to resemble the 6.3 harness.
Well those were the most important changes made to that 4.5 harness to work properly with the 6.3 engine train.
If you have a similar project please contact me through the regular channels and I will be more than happy to come with an engineer solution to your particular case.
Best regards
Eng. Leonardo Peterssen
Here some photos of the project
https://www.icloud.com/sharedalbum/#B0QGd59qiGR6Bxc