Backup wiring

Whose wiring harness did you get?
Did you specify that it was for a four speed?
Cars with automatics had the reverse switch mounted on the steering column (or on the linkage in the case of a floor-shifted automatic, which will use a small extension harness to connect), so that is most likely where you will find the connector for it. You will need to fab an extension harness to go to the switch on the four speed; or contact your harness manufacturer and see if they offer something.