Wiring harness compatibility.

[T.Hanson]

Is the answer just pain staking tracing wires, colors, and learning ? Most parts drawings list the wiring harnesses NLA to make part numbers irrelevant.

I've wondered if the ECU's, aluminum boxes with all the pin outs in the glove box, are all the same for '79 to '81 e12 (and e24). Only because my six cars over the years have had those units sometimes replaced, with a 633 written in marker on the box, running a 635 just fine.

So many little pins, into the big plug, big wire bundle through the firewall. To discover that harness is fuel injection related. It meets with the second harness at the combo relay,...that differs from year to year in connections to sensors and throttle switches, aux air valve, nemo version or valve cover, etc.

Looks like a nightmare for anyone but a wiring guru genius, if one wanted to replace a thermostat housing with more or fewer sensors, or a nemo with a valve cover aux air.

[Mike W.]

There was a 79 only ECU, but both it and the 80/81 one found in 633/733s will all interchange between cars and applications. Some of the wires are different lengths due to things being mounted in different locations, but really it's all the same.

[T.Hanson]

Thank you, as usual. I figure to leave what's there alone, but if I got to fooling around, maybe have some idea when to wear a helmet turning the key.