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If it's a DC pump the alarm probably just turns on a relay that swaps the input polarity of the motor.

Yep. It comes with a relay and I wired it to another DPDT relay. It's supposed to go on the carn horn terminal instead.

I love how older vehicles have really simple wiring.

Seems like a really complicated kill switch.

Exactly. Every fuel pump has a ground that you can put a switch on to kill it. No need to run it in reverse.

Except old engines with mechanical fuel pumps like the GGP has

GGP said it was an aftermarket electric fuel pump

Both; the mechanical fuel pump doesn't work so well, so the engine has issues starting, so i added an electric pump. At that point it was easy to also add a DPDT relay since I was taking the whole thing apart either way

lol, right, sucks when they don't start.