When in ign2 (start) the coil needs to be fed (full voltage bypassing the ballast) and the "point" of the ECU connector needs to be fed (4 pin ECU) plus another pin on a 5 pin (stock type) ECU. Take off the yellow "sol" wire from the starter relay to temporarily disable the starter (just to eliminate the noise/distraction and battery drain) and have a helper hold the key to "start" & you under the hood see if these 2 points (+) pri coil terminal & the "point" of pentastart connector) (3 if 5 pin) are getting fire. Sounds like classic ballast prob but not always and I had that recently on a stock 5 pin ECU truck and it was the ECU.