What are these 2 connectors for?
So far as the others, do you have a 74 service manual. If not send me a PM and I can get you one, for the cost of mailing a usb memory stick.
So far as the brown/ yel not sure. I found reference to a diode in the seat belt crap connected with maybe the back up lamp switch. (B3-20-BR/Y)
What color wires are in the connector with two wires coming out?
Maybe disconnect battery ground, hook ohmeter to the unknown connector, and random probe the bulkhead connector for a/ some hits