Why 10.7 volt input at ‘71 Duster instrument panel?

That is NOT normal Make REALLY certain you are on the correct pin, that is, that you are not reading it "backwards" or backside of plug vs front side--mirror image.

I would get right down to your ignition switch connector and check V at the "run" line and whatever else is coming out switched for "run" and "accessory."

Don't ignore the easy/ simple stuff. Make certain your tester is accurate, and make sure the other end is well grounded