- Remove the white wire from the glow plug relay and cut off the terminal.
- Install a crimp or wire nut on the end of the bare wire, tape it up, and tuck it away so that it is secure - this wire is no longer being used.
- Cut the blue wire for the wait-to-start light halfway between the electrical connector and controller.
- On the end of the wire that goes into the controller, install a crimp or wire nut at the end, tape it up, and tuck it away - this wire is no longer being used Crimp roughly 12 inches of wire to remaining blue wire and install a ring terminal on the other end.
- Plug the wire connector into the matching connector in the wiring harness, then
- install the other end to the terminal on the glow plug relay that you removed the white wire from - this will allow for your wait-to-start light to illuminate while the glow plugs are being manually cycled.
- Run a wire from your momentary push button switch (do not use a toggle switch or switch that remains activated after your let go) to the terminal on the relay that you removed the white wire from (where the blue wire should also be installed).
- Run the other leg of the momentary push button switch to a good ground (preferably to the frame or engine block).
HOW THE MANUAL GLOW PLUG SWITCH WORKS
To cycle the glow plugs, turn the key to the "run" position and then hold down the manual glow plug switch for 7-10 seconds, then release and start the engine. Do not cycle the glow plugs for more than 15 seconds at a time. If the glow plugs need to be cycled again, wait 5 seconds and repeat as necessary.
The modification works because it controls the ground for the glow plug relay (which receives power anytime the key is in the on position, but the glow plug controller normally switches the ground).
When the button is held down, it completes the circuit and activates the glow plug relay, bypassing the controller and supplying power to the glow plugs for however long the button is depressed.