Well I never had a problem w/ the Grid heaters until today.
I went out to fire the rig up it is 22* out here.. and I noticed the "Wait to start" light did not light up? So I cycled the key on/off to see if it would turn on.
But no luck, I cranked the key and the engine started and idled roughly down to a stop.

I now have it plugged in and waiting for it to warm up a little.
Any idea on why the grid heaters, or the "Wait to start" light would die off?

-Jared

 

Theres a temp sensor to tell the computer if it should turn on the heaters , then the relay to heaters , fusible links from batteries , having a wiring diagram is the best , maybe a search will bring that up .
From reading it seems like the fusible links & then relay is the most common .

 

Like John says, there is the intake air temp sensor just to the rear of the grids on the intake. Since your light isn't coming on i would suspect that since the light will come on even if the relay isn't working.It is the sensor that tells the computer to activate the grids. Then there is a smaller relay on the firewall beside the brake booster that controls the two larger relays down on the left inner fender.

 

The cheap Hayne's manual has a very good section on checking the complete grid heater system. Well worth the money.

 

We have an haynes manual down at the shop for the truck.
I was just trouble-shooting.
I searched on here and read about the fuseable link.
I checked all my fuses inside the truck and I had a blown 10AMP for the "Engine" not sure what all this runs. But I replaced the fuse and started it up and blew it again so I must have a shorted wire somewhere that I'm going to search for tomorrow.

I also lost my tach/speedo
but all other dash lights/signals work.