I installed 6 relays on my car. One for each AC-heater speed ( four ) and the other two for headlights, but all relays are into the cab hidden down the dash without cut a wire ( I didn't want a single relay visible ) All just relocating the stock terminals from switch plugs to relay plug and jumping a wire ( same color ) to continue the original trace. But I made it mostly to save switch points. My headlights are halogen sealed beams with sucks more power than regulars, and the AC blower switch plug allways got melt on my 74 due the poor contact made inside. I, still using original wiring and terminals to handle the power. I did of course the complete wiring and terminal mantenience of course, and replaced terminales where needed.