How would I add a relay to turn on a new device when the car is on?

[quote=“Freek,post:2,topic:27716"”]

what year 240?

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It’s a 1990. I supposed I posted before I really thought about it, but I should try to find a wiring diagram, see where the wire would have originally originated from within the car, but it looks like the interior was completley stripped at one point (theres a new carpet in there) and for what ever reason, the switch wire was never fed back in to the radio harness.