It doesn't just happen in ACC. Its actually worst when i'm the engine is running. i'll try head light thing. this truck used to an alarm too. which isn't in it any more. but is still all wired in all crazy. under the dash there is a bunch of wire all balled up. with cut spots all over. I saw a phone jack in there. Which i believe hooked into the back of the alarm unit. but seriously i'm gonna check the wiring maybe change some.