i have a 85' 6.9l diesel. i was driving the truck today and i saw the glow plug light come on. it was about a 100 miles till home so i drove thinking nothing of it because the switch was off. when i got home i removed the glow plug controller on the back of the block. it is toast. full of rust. But i think my glow plug contriller is bypassed to a switch on the dash next to the glow plug light.

Help?

 

When you use the switch for your glow plugs, does the WTS (wait to start) light come on?

From what I understand ... if the light does not come on, then chances are that the glow plug controller is not in the system at all, and the failure in the ON position doesn't mean anything (besides an annoying light being turned on). On the other hand, if the light does come on when you use the switch to the side, then the glow plug controller is still part of the system, and now you probably have burnt up glow plugs.

Check your glow plugs to see if they are good. If so, don't worry about it.

 

On the 85 system, the power to the light is from the glow plug relay glow plug terminal.

If the light is on, the glow plugs are getting power.

Two large AWG orange/white or orange/green wires on the relay behind the passenger side battery on the inner fender well.

Under the orange wires there is a black/pink wire that goes to the "Wait to Start" light.

Best option in my opinion, eliminate the controller and go full manual control on the glow plugs.
Downside, if other people drive your truck getting them to understand 10 seconds glow time is hard.