? Intermintent cranking issue 2003 lb7
 

Does anyone have any suggestions.
Intermittent cranking. No codes. Checked starter, ignition, trans neutral safety. Fuses and relays. Something seems connected with glow plug. If glow plug light illuminates truck starts otherwise no crank. Presently no 12v at signal wire at glow plug relay. " 4 prong plug yellow wire should bring 12v for 10 seconds "Tracing wire back thru harness to computer. Or where it comes from. Have continuity up to bale connector. Not proceeded any farther yet. Thank You for any insights