You should wire a momentary switch to the one of the relays, the relay will already be wired to the glow plugs. You need to disconnect the glowplug controller. There are 2 relays, disconect the relays from one another. Then wire the switch to the relay that does not go through the drop resisitor. Be careful to only hold the switch a maxium of 5-7 seconds. Upon starting, you can press the switch on and off a couple times, this will simulate what the glowplug controller would be doing.