a puff of smoke and now nothing 69 valiant electrical issue

see picture in 31. that gauge the needle went all the way right and disappeared. I reviewed the diagram but i am confused. there is literally no power anywhere. No headlights, no door dome, horn, etc. I used a light meter to check if the battery fried and it is showing power. A restoration mechanic said the whole cluster was shot and the nuts on the back were corroded/worn like someone had busted some of them off and that it was from the electricity coming back when my son hooked the hot wire to one of the bolts that is not the ammeter.