I have been plugging in my truck anytime it is below 15 degrees. I plug it in on a timer for about 5 hours and when I unplug it and go to start it the glow plug light never comes on. Here is my problem (QUESTION), this morning it was below zero ( -3 degrees with windchill -10 degrees) I went out unplugged my truck, popped the hood, unplugged the cord, shut the hood, and jumped in the truck to start it when I turned the key over my glow plug light flashed for a second and then went off. I started my truck and the gauge did go up above 160, so I know my block heater was working. Why would the light still come on after being plugged in? Is it possible to have cooled back down with-in that minute of unplugging and getting into the truck? Sorry for the long thread, any comments would help. Thanks.