You're probably grounding out somewhere else then. If you don't do a lot of wiring, then I'm gonna guess it's around your alarm under the dash. Most of the installs I've seen rely on vampire clips. Those are usually a crapshoot and after a good amount of vibration may start chewing through the wire. Had a similar problem before. Try just looking under the dash and wiggling some of the wires around, see if anything flickers.