I got my switched power in my car from the fuse box under the hood, you can get a connector that will latch to the fuse and give you a male spade terminal to connect to. I would be very carefull what wires you even test with a test light. I was looking for the power window turn off wire in the rear driverside door and when I touched my testlight to one of the wires the onscreen display said "brake fluid level low visit workshop". Needless to say I gave up on that project real fast.
