I'd take off the starter solenoid wire to termporarily disable the starter (to keep from running the batt down and for the noise distraction) and have a helper hold the key to "start" while you check voltages to the ballast, to the ecu, to the coil positive primary terminal all of which need fire. Start at the bulkhead and work downstream or if your good there go back toward the ign sw. www.mymopar.com should (dont know if they have truck apps) have the colors to help you. (temporarily) disabling the starter will skew your readings as it is not now a normal cranking voltage reading(s) but you have an outright "open" somewhere that'll be apparent when you test that particular connection. Is this an OE 4 terminal ballast/5 pin ECU? If so 2 pins on the 5 pin ECU need fire. Grab your VOM