What he is trying to do is, get a visual indication when the GP relay is on.
I understand this because I understand the circuitry involved and from what he posted.
I hate to say this so boldly but, If you don't understand what someone posts, then sometimes it's better off you post no reply at all.(unless you want to understand them)
Many people are not just parts changers only, and they like to either understand things/diagnose them, or actually modify things to suit their desires.
So, since the relay is fed 12v constantly and the light blue wire supplies ground(to actuate the relay), there is no 12v + fed into the cab that you could tap into for this idea.
Also, since the controller has a voltage sense wire on the output of the relay, you really don't want to ad much more load there. You could use an LED that is safe for 12-24 volts and add it to the GP load(relay output). You could tap into the orange wire at the controller for this to get the glowplug + voltage.
An even more useful idea would be to add a voltmeter to this orange wire. Then you could see the voltage drop and know if you have a bad GP. This would not work if you have done the resistor bypass.
