Rallye Instrument cluster voltage limiter - 68 Barracuda

The circled item is a radio noise supression cap, as the original limiter clicked rapidly off/ on similar to a turn flasher.

You may well have damaged/ killed your gauges.
Could you explain how exactly I killed them so I know in the future?

With the suggestion that the original gauges are now fried than I need to start considering replacement options. I'm guessing that installing a new digital regulator as above will not fix them and will need to source replacement ones or look into replacing the whole dash with aftermarket gauge kits.