75 Duster electrical boxes

You really need a service manual. I have a 76 "somewhere" I'll see if I can find it. Part of the info you need 'may' be in the 73 shop manual which you can download from MyMopar for free

Also, I posted the later wiring section in the manuals thread.......Some of it might be in there

Free service manuals

Here is the wiring we scanned for the 76 wiring

I BELIEVE it is Trailbeast hosted this:

http://www.letsgocomputers.com/docs/76wiringAbody.pdf

Start with about page 9 of that pdf

The box on pass side is EGR time delay