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I'm not sure about the 2005's but the older ones (eg 2003) have a "customer access" wire on fuse # 29 which is a 10 Amp circuit. Locate your OBD II plug under the dash and follow it's wire bundle up towards the radio. You should have a white with blue tracer wire which is capped off with a black heat-shrink piece and that is taped to this wire bundle. Power is on in "RUN" only.
For my air horn, I tapped into one from the tow package. It runs right along the drivers side frame rail. I believe it was yellow. Use a multi-meter on the power plug at your hitch to determine the color and key on/off state.
I thought this was exactly what I needed, but either I didn't find the right wire, or it isn't quite what I'm looking for. I found a white wire with a blue trace, in what I think was the right location (behind the "ash tray"). It was a stub, and it only comes on when the key is in "run". However, the voltage isn't constant. It seems to increase with engine temperature, although I can't be sure of that. Seems like the voltage starts around 11.5V, gradually increases, then tops out around 13.9V.
I guess for many applications this would be fine. I need the power for my radar detector, however, and that seems to be voltage sensitive. Below about 12.? V, it behaves crazy. I could almost live with it, since the whacky behavior only lasts a few minutes (or less?), except part of the whacky behavior is incessant chirping. Drives me nuts.
Anyways, did I find the right wire, and this is what it does? Or did I find a different wire?
i have upfitter switches on ebay. and then you would still have three switches to do whatever else with the upfitter switches only go hot with the ignition on. and there is an article here somewhere on how to make the switch momentary.
Thanks for the offer. I have factory upfitter switches, and that was what I was planning to use originally. Researching how to tap into them I came upon this thread, and thought this was and even better deal - on only when the key was turned to "run". I guess I'll go back to the upfitter switches.