Installed msd ignition box and dizzy. Now wires under dash try to get hot

You seem to have amps (amperage, current) confused with voltage It is charging at 15V This is commonly caused by voltage drop in the harness. "The path" from battery to VR (refer to the diagram I posted above) is battery---fuse link---through the bulkhead on RED--to and through the ammeter, out on the BLACK--to welded splice---to ignition switch connector--through switch and back out switch connector (ignition "run" dark blue, IGN1) back out through the bulkhead connector---and branch off to underhood loads, the alternator field, the VR, the ignition system, etc etc.

ANY DROP in that path will ADD to charging voltage

Also DROP in the GROUND will cause this. Make CERTAIN battery is WELL grounded to body, and VR is clean and tight to body