BRONCO II from h***

Last night, I was driving my 1986 BroncoII. (sometimes that is a feat in itself)While driving, I had to dim my head lights, as I pulled back on the dimmer lever the engine backfired. I thought that it was a bit odd, and just maybe a coincidence. When it came time to put the lights back on bright, it backfired again. I tried this several times, dim, bright, dim, bright, and each and every time it backfired. Now for the odd part (as if this wasnt odd enough), it only backfired if I was @WOT. Has anyone else had this issue or heard of any thing even close.

It could be that the throttle linkage is hitting something at WOT.