They make an adaptor that allows you to slip a connection in the fuse relay box, such as the radio/cigar fuse.. That's basically your "Acc" ignition circuit. So you don't have to dig for the right wire. just make sure you use the right side of the fuse. I did something similiar. I hooked up a LED lighted switch coming from the battery (fused) that goes TO the radio/cig fuse. By doing this I can override power to my radio and pwr outlets front and rear without having to leave my key in the ignition. so if I want to leave the radio on in the driveway I don't have to worry about someone stealing my car.
Also, I did an "F.U. back off" light as I call it. <img src="/forums/images/graemlins/smile.gif" alt="" /> Although I just joke about it being called that. But I'm not saying I wouldn't use it on buttholes that follow with highbeams.. I have mine mounted higher up though. Mine's mounted on the top bar of the spare tire arm along with my CB antenna. Unfortunately, I did a temp cheapie job: it's directly connected to the LR back up light and so it's dull and I can't switch it on when I'm going down the hwy. I was going to put a relay and switch on it, but I didn't have enough wire to run the length of the car nor the relay. But I will this spring