you can ohm out the GP at the VC...if its a bad wire or GP you will beable to tell..if there good you will need to trace the wires back..i think the X does not have a GP relay..its done though the PCM...here is the pin out and specs..

Pin Out
G G I I C I I G G
G=Glow Plug +
I = Injector +
C= Injector Common
***The injectors fire with a 115VDC signal from the IDM do not pierce to wires to test.***
Ohm between "I" and "C" to test the injectors, should be less than 5.0 Ohms
To check glow plugs Ohm between "G" and battery ground should be between 0.1 and 2.0 Ohms