If memory serves...the GP relay sits on top of the solid state controller----it has a wavy metal plate---- the GP relay gets power from the fender mounted sol that also feeds the starter when latched by the key switch in start position.
Off that same fender mounted sol should be two {yellowish if I recall} 12 ga wires that go to the cannon plug on the right fender and from there go to the GP relay. This is a known weak link due to the current that flows thru the smallish wires and plug---trace the two wires from the fender so to the GP relay, they should be 12 hot constant--remove them from both the fender sol and GP relay and replace with some 4 ga stranded with good copper lugs soldered on...connect to GP relay FIRST then to pos side of fender mounted sol..or directly to the right battery pos terminal.
You can install a 250 amp MEGA fuse inline for peace of mind but I ran mine for years without one without issue.
Your GP's will LOVE you for doing this