That wiring leg (from the positive bat terminal to the starter relay) also contains the fusible link, so be sure to install it properly so you do not get a short someplace and toast your new harness. There should be another heavy gauge wire from the firewall plug to the positive battery terminal on the starter relay to feed the fuse block, ignition switch and the rest of the passenger compartment wiring. Those two leads go to the big terminal on the relay. There will be a third light gauge lead to the ignition switch to energize the relay, opposite this lead there is another light gauge lead from the neutral safety switch to ground the circuit that energizes the relay. There is a 5th heavy gauge wire to the starter solenoid that is is activated by the energized relay.
Dave