ignition trouble shooting

Well I'm guessing but I think there is a huge hi-resistance connection somewhere between the battery and the ignition switch. Or possibly a huge grounding issue between the battery and the engine block. Or a huge problem in the battery.

I would start by load testing the battery. If it tests OK, then charge it up and clean the posts and the cable-terminals. If the terminals are not original type one piece, then remove them from the cables and clean the grunge outta there. Remove the negative cable from the engine and shine the connecting surfaces. Finally make sure the body grounds are there and connected cleanly.
Now we can start the diagnoses.