the problem with most, if not all clarions is that they look for a pulsating ground... such as the parking brake where they tell you to put it... my buddy has the same unit you have and he just loosened his parking break cable so it didnt work (no one around here ever uses them anyway) then he wired it to the brake and took the bulb out of the dash for the parking brake light... seems like a hack way of doing it but it works and has no effect on the truck... it was an "off the record" suggestion from a clarion rep