Why 10.7 volt input at ‘71 Duster instrument panel?

When you say with the ignition "on" you mean in the "run" position?

If you have a points distributer and the points are closed there is a good draw, look at the ammeter.

Try turning to accessory and checking again.

If it's the same then you will need to track down the bad connections.

That's a lot of voltage drop.