Also if you aren't already aware, '76 power feeds were wired differently than early cars. Ignition is the same.
Do it two stages. Battery fully charged.
1. Put the key in run and measure voltage at all four terminal postions on the ballast (assuming its factory dual ballast).
If there is a break in either of the ballast. Stop there.
2. With a helper, measure the voltage on the coil side (J3 in drawing below) of the ignition with the key held in Start.