Early d-Jetronic fuel injector short.

Hello all. I'm in the US living in Oregon. I've owned my 1974 450SL for a long time and a few years ago it started to run rough... missing. I researched everywhere, replaced all the usual suspects... plugs, wires, distributer parts. Checked trigger points/ contacts. Nothing would work until I replaced the fuel injectors and Wow it ran great. Well most recent I let someone borrow the car and brought it back with a substantial misfire again. I've gone through all the usual suspects again including replacing the injectors but still can't figure out the problem. What I did find is that on about 4 of the injector wiring connectors, the voltage side was grounded. I've cut back a good portion of wire harness looking for a short but nothing is obvious. I've reached out to a couple folks on line but no real answers to how or why some of these injector voltage side would be grounded. I'm pretty sure not all cylinders are firing leading to the misfire. Can anyone shed some light on how the actual voltage is generated to the injector harness. I know the trigger points direct the signal but they electrically checked out. Everything on the driver wheel well seems to be OK. PCM? Any thoughts that could cause a short to some of the injector wiring, Anyone else had this problem.
Thanks   

Hi Unknown,

we would appreciate your first name to be able to adsress you directly.

ECU generates pulses for injectors. See injector groups in Appendix B. It will teach you that there are 4 and if all injectors on one side of engine fail, it is not an issue of ECU but of wiring harness.

Sorry it's Frank Brenckle. Thank you for the quick response. So I've got 3 on the passenger side and one on the driver side that appear to be grounded. Either way your thinking more of the wiring harness. Is there any part of the harness that could be more suspect then other areas. Known areas where it could get damaged. There is a lot of wiring so trying to help narrow it down.

Hi Frank,

replace whole engine wiring harness. Everything else makes no sense.

Hmm interesting. Well I guess I'll be trying to source one then. Thank you for your help and insight.