so ive been waking up early for work lately and i noticed my wait to start lite has yet to come one and im sure it should have becasue we have had some colder mornings. from what i remember last winter if its below 45 oF then it should be coming on. i want to know if theres a way to test them to make sure the grid heater relays and the grid heater itself are still working. as i remeber in the summer time i think my brother accidently hit the relays and they arc'd for a split second with the truck off. is there a fuse or anything connected to the grid heater relays?

 

Now would be a good time to figure out how to put them on a push-button that you can control yourself.

Or, just do like I have and dis-connect/ignore them.

 

Nick, is yours a '91 or a '91.5?

 

I believe it will be a 91. It's non ic and a 727 trans. But I am unsure if they offered that in 91.5.

 

Unplug the sensor in the intake manifold and turn the key on. If the system is OK, the WTS light should come on steady and you should hear the relays clunk. After 20 seconds the relays should click off and the WTS light should start flashing.

If it does all this and you are not getting a WTS light on cold mornings, then the sensor is bad. The grids should operate any time the manifold temp is below 59 degrees. A 50 degree overnight low might not drop manifold temp that low, though. Depends on where your truck was parked and how late you came home.

This diagnostic check covers all non-intercooled trucks, but some '89's don't kick on the grids until 15 degrees.