first off, i'm new to the site, and well, today we installed a new alpine unit in our 05' dually and we turned the ignition on, and after maybe 15 seconds the truck automatically turned on, does anyone know if this has always happened because we never noticed it and how do you disengage it and finally will it affect anything while driving or anything?

It could be (very odd) that the "Alpine's power antenna lead" was mistakenly hooked up to the ingition's starter wire or maybe to the alarm's remote starting funtion...(if you got an alarm w/ such feature)

tip: the "power antenna lead" is usually a BLUE or ORANGE wire on most stereo head units.

Good luck!