been out hunting this week. i noticed at least twice, when the air temp was in the mid 50s and my truck had been sitting for at least 10hrs(and unplugged), my grid heaters didn't kick on(wait to start, idle, or, low speed driving). someone suggested that there might be a fuse link in the wire from the battery to the relays, but both had voltage thru the wire when i checked it with a DVOM. what should i check next? or am i jumping the gun, and its not cold enough for the ecm to start the grids? ISX does the 12v PCM run the grids? didn't you wire a switch for those?