With a Ford that has a separate starter motor relay, the relay has large copper studs. Select the stud on the battery side of the relay to manifold extra wires out. Using the battery post clamping bolt is bad juju. Too vulnerable for corrosion, the clamp bolt and nut should be reserved to do only that and nothing else.
ANY TIME A LARGE RELAY HAS A WIRE RUN TO IT VIA A DASH SWITCH, THE SWITCH, AND WIRE BECOMES A HUGE LIABILITY. Vulnerable.
The solid state controlled relays, the ones that are contained in one unit not a relay and separate control box, use almost no power. Unlike the ones that have separate boxes.
Either Blue Seas or Sure Power is a good "SMART SOLENOID"
When I was in business I supervised Armando and repaired a few tens of dozens of failed relay/switch charging relays. They are a POOR CHOICE for doing this kind of duty.