There always seems to be some confusion about the glow plug system and the wait to start light on the 7.3l Powerstroke. The Wait to start light is controled by the PCM, but has little if anything to do with the operation of the glow plug system. It is more of a timed idiot light then anything. Also, just because the WTS light comes on, this does not mean that the glow plugs or glow plug relay is working.

So a lot of guys install a glow plug warning LED (GPR-LED)...

Here is a quick video that shows the difference between the WTS light and the time that the glow plugs stay on...

YouTube - Glow plug light

To install this LED is very easy, even the most novice electrical guy can handle this in your driveway in about 30 minutes...

First go to your local autozone, Radio Shack or Napa and pick up some 12-14g wire, about 10' is more then enough, and a LED of your choice. They have tons of different kinds, sizes and colors but get one that is a complete unit to make this easy, not one that requires a Diode or Resistor...





Once you are home again pop the hood and locate the Glow Plug Relay (GPR)... It is the furthest back relay if you have a 99.5 and up. Take a look at this picture so you understand the different posts on it...



You want to run a wire from the #4 post into the cab and to where ever you want to install the LED, add a small fuse to this line before you go to the cab (I have not done this, but its good practice).



There is my Red wire for the GPR-LED headed to the cab and up the A-pillar.

For your ground wire, depending on where you install the LED, you can ground it with your gauges, to any metal in the cab or back to the battery (waste for sure!!!)...

Now when ever you turn the key on, and the glow plug relay closes, this light will light up. If your having hard start issues and this is not coming on, well you know your relay is bad... If your having hard start issues and this light is coming on, then you know its not the relay...

Feel free to hit me up with any questions...