Those Cannon type connectors, at least the ones used in aircraft take a special what I call a 360 deg crimping tool. I have the ones needed, fortunately. Glad to know I am not the only one who forgets to put covers and fastening rings on harnesses. I forgot one on a 40+ connector., then had to disassemble and re-do. I finally taped paper notes to any cable that had a multi part connector, and that really helped.

I'm with you on wiring stuff up and finding the part of the connector that I should have threaded the cable through sat on the bench! Arrrrggggghhhhhhhhh!!!! I bet everyone has done that at some time or another too🙄