How olds the battery? How cold has it been, low battery will cause nasty things to happen. I'd check the battery with volt meter. Also unhook the battery for 30 - 60 seconds and try to honk the horn while its unpluged. Hook it back up and see what happends. I assume some one elses is driven ur truck while ur away, I'd ask them if they ran over any thing that they know of. Maybe the ac power wire has come loose and flying around causen it to flash as it makes contact. Also check the codes. If there is a code, we can help much more!!