Check your ground-wire. I had a similar problem when my ground-wire corroded and the ignition would only ground through the starter when the key was in the "start" position.

89 xcab 4x4 22re. 1.5" BJ spacers, 3" shackle and AAL + fender trim. 33x12.5 R15 MT/Rs, 15x10 rockcrawler streetlocks. 488 yukons by ZUK, detroit rear and true-trac front. 2 1/4" cat-back exhaust. Redline gear oil. Rear bumper by bentup.com.