I'm getting a high mounted LED third brake light any day now. Can I wire it into the existing brake light wires or should I go directly to the brake switch and wire it on dedicated power leads?

Never have, never will cut a factory harness wire.
Exceptions are repairing hacked shit done by stupid dumbasses, broken connectors and repair/custom engine harnesses.

Run a wire to the tail lights, use a double spade connector, done.

No wires were harmed in giving this advice.

I ran my wiring directly to the driver's side tail light. A couple of 2 into 1 spade connectors made for a splice free wiring job. While you're at it, take a look at adding a strobe. I used this, which now seems to be unavailable. Bob

https://www.amazon.com/Vehicle-Flasher-Modu...s/dp/B00FADDOL4

Curtis,

I agree with Mark Henry & the Newbie (WTTC BTW) - run to the taillight, & IIRC you can pass it through where the main harness goes into the rear trunk on the driver's side, & where it passes into the cabin, behind the backpad & roolbar pads to the light.

If you got that GoWesty one which I suggested, then there may be enough of a lead that comes with it to reach, but trial it from the outside of the car first & add a coupla-three feet extra for the maneuvering around the body. If too short, then get some matching wire gauge/colors, in-line connectors with shrink-wrap to extend them hopefully within the trunk.

If it's another 3rd light, then I don't know how much wire they supply, but process is the same.

Good Luck!
Tom
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Thanks guys!