Engine bay wire harness electrical connections.

it shouldn't start with transmission in reverse

1976 Hazards are on their own feed. See the link I previously posted about them.

For other cicuits you can use the ammeter to see if current is flowing from the battery.

Starting sequence illustrated here.
Battery needs to be fully charged.

This shows the concept of how the relay works, but on a '76 the junction to the key switch is spliced into the battery wire.
How the starter relay works.