Dear friends
Just delivered the wiring harness set shown on pictures to a customer in Alabama who has a w113-250SL-LHD-MANUAL.
This simple project for me, had some peculiarities that may be of general interest in our community. Many of them thought around driver safety.
- Inertia switch on the trunk We added to the rear harness a FORD OEM inertia switch (good quality), which delivers a constant ground signal to a fuel pump relay added on the driver footwell. In case of accident/impact, inertia switch cuts ground signal, causing the fuel pump relay inhibition
- Fuel pump relay. On a w113 / w111 mechanically fuel injected car, electrical fuel pump runs continuously as long as ignition switch is on the run position. This is a safety hazard according to nowadays standards. Mercedes corrected this approach on later models with k-jetronic or d-jetronic fuel injection systems, by adding either a control relay for fuel pump with certain degree of intelligence, or by having the engine ECU have full control over a standard 4 prong fuel pump relay. Therefore on this project, I decided to retrofit some of that logic by adding the w123 (6 cyl) fuel pump relay which has many control ports as: a. Starter T50 signal; b. T15 ignition signal; c. Tachometer signal. And of course d. Ground. Any of the first three control variables will have the fuel pump running for a certain period of time. T50 starter selenoid signal will activate relay while cranking; Tachometer signal (from coil negative post) will keep pump running as long as RPM pulses are present; and T15 will preload system for 5 seconds once triggered
Of course, as the control relay may fail, as a preventive measure, a jumper connector has been provided to plug on the fuel pump relay female connector in case of need.
- increased power handling capacity . As on many of my project harness, this one was modified to accommodate a larger alternator with internal regulation as Bosch AL69X, eliminating one weak point and opening the possibility of installing later new consumers as could be an AC system
- simple alarm system. A simple, but effective and reliable alarm system has been added to main harness, in the cleanest and most professional way. Main harness can be reversed easily to original state since everything has been done without splicing any original cable. The alarm has control on the coil T15 supply and over the fuel pump relay
Some other simple goodies were also added to this harness, as brake fluid sensors, and connections for a modern TTS (thermo time switch) all looking forward reliability and safety.
The final project photos can be seen here:
https://www.icloud.com/sharedalbum/#B2O5ko8dMGfmkAXBest regards
Eng. Leonardo Peterssen
Www.wiredoktor.com
