Here is a 21 page FREE PDF document dedicated to educating you on how the wiring works for swapped N52/54/55 engines into your E30 or E36. This includes how to read wiring diagrams, both the old versions (E30, E36 vintage) and the new diagrams (newtis.info type wiring) such that you can get the information you need to turn that key and start your swapped BMW!
This guide includes connector reference designation labels annotated for both MSD80 and MSD81, labeled wiring harness connectors for engine harness layout, but most importantly, how to read wiring diagrams, specific to any BMW you need to understand.
This is a free download, just for you, PDF Format to view and enjoy. So read through it, understand what you may need to know. If you would like to take a bigger bite, feel free to buy the entire guide for either the E30 or the E36 chassis. Good luck and happy reading!!