Advice Sought on 1965 Mustang Ignition Start Issues

My 1965 Mustang now refuses to start once I turn the igntion key to fire up the starter motor. Oddly, it also seems to lose power to the instrument panel and radio when I turn the key – I’m not sure if that gives any clues. I have now replaced the starter motor, solenoid and ignition switch – all to no success. Bypassing the solenoid with jumper leads results in engagement of the starter motor so I know that’s OK. The new solenoid is an orginal Motorcraft replacement so that’s unlikely to be the issue. The next culprit could be the neutral safety switch that governs starts only in park or neutral gears and I’ll investigate alignment issues and, if not that, then replacement if needed. However, does anyone else have any insights or experience as to what else could be the issue? Many thanks in advance for any advice.