Try testing the switched power wire that leads to your radio. It should be 12 volts. It has a delay, but will cut off when turn the car off and open your door. I used mine to activate relays for a fog lights harness and LED DLRs. Since it only activates the relay, there is no constant current draw. Try the Haynes Repair Manual for your model year. It has a complete wiring digram in the rear, and will tell you the color of the power wire.
2006 GT, Strut Tower Brace, Gas Hood Struts, FR Intake Plenum cover, Metal Fuse Box cover, Moroso brake reservoir cover, Rear shock tower brace, Front Bumper Lip Spoiler, JVC DVD Head unit w/ back-up camera, satellite Radio and USB input, 2 - 12" sub-woofers, 4 - 6"x8" speakers, 2 - 6.5" speakers to replace the door subs, 3 amplifiers, LED lights under the hood and in the trunk, chrome e-handle on parking brake handle, chrome cup holder trim, and trunk lid cover with running pony emblem.