Just something to check, since you mentioned nothing seems to work ...
on an otherwise nice '66 300 HT I once had the main power connection at the bulkhead had fried internally, before I got the car, and why it had been parked.
A pretty simple fix, but the PO had given up and parked it, and it took my simple little mind a while to figure it out ...
might be worth your time to pull the connector apart and clean things up.
Nice convertible, one of the nicest cars I ever owned was a really clean nice '68 Newport convert.Should have never sold ... well you know how that line goes.
