The following truck wiring diagram is originally scanned from 1965 Chilton’s manual. Should you have an all original truck with overdrive, this diagram should be usable. This manual contains a diagram for wiring a split control setup for your T-85N transmission. This can be used for one you’ve bought outright and have no original circuit for, or modifying the one you already have. The DPDT relay is Double Pole Double Throw relay.