accessory wire on new gm vehicles.

hey there guys, i need a little help here. im having trouble with all the new GM vehicles. i connect atleast 5 systems a week on GM vehicles 07+. everyone for some reason wants to stay with the factory deck cuz in reality no one wants to pay $140-160 for a wire harness. the only problem i have is that these vehicles dont have an accessory wire. i already used a pac SOEMT line output converter with a remote wire but it doesnt help. the amp stays on for a bit when the vehicle is turned off and then a couple of seconds later theres a loud thumping noise for a couple of seconds. i understand its because of the retain accessory. later i found that by the foot brake, there is a switched accessory at the fuse box. i was happy to find that so i called all my customers back and re did there remote wire to that fuse box. well yesterday one customer came back saying that his truck literally stays on until the door opens. i understand the radio stays on but not the truck. the guy literally turned the truck off, took out the key and the truck was still running. he opened the door and the motor shut off. thats wierd. so can anyone please help me out here. thanks in advance.Accept only the best, No Substitutions!

Have you tried tapping the 10 amp fuse in the top left corner of the fusebox mounted on the left end of the dash?

they are all constant. none are switched accessory!Accept only the best, No Substitutions!

hi, any particular gm vehicles you are referring to?

pretty much all the 07+ silverado/sierras and escalades. 09+ camaro, impalas and any other gm vehicle that would use an PAC OS2, OS3 and OS4.Accept only the best, No Substitutions!

pink wire at the brake pedal.A DMM is a beautiful thing.

MECP Advanced Installer Certified.

There should be a brown wire in the ignition harness that is an accessory. It isn't high power, so you would need to use a relay to use it as a power source. But for an amp turn-on it should work fine.