engine forward working harness alternator.

I've been scratching my head at getting my alternator into my 74 duster , it was an original slant six with a 318 swap done prior to when I got the car. it only had the motor no accesories and trans in the car and I found the original wiring harness in the trunk got it put back into place and realized it is missing the alternator side of things so I've been attempting to wire it in myself but just can't quite get things right. Has anyone ever had to purchase just this section before ? If so where at?