I just swapped my M42 motor over to my 316i. I left the fuse box alone while i fitted the harness and hooked it up to the ECU. that round plug has a couple less pins then the amount going into the harness. just to rephrase, i left all other wiring alone. it would be the original 316i stuff.
+ when battery is hooked up and no key in the ignition the oil, batt, warning, etc lights are all on. only way of turning them off is unhooking the battery