Why 10.7 volt input at ‘71 Duster instrument panel?

Ken71Twister said

Also - with the engine running - the voltage at the instrument cluster plug is over 13 V. I also found another pin for dash lights that reads 11.9 V with the engine running. Maybe I’m ok with the voltage issue. I didn’t run the engine earlier because I was in the garage and had a gas leak at the carb check valve that I’ve since fixed.

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OK, the most important part is the cable fitment and alignment to the instrument. That square port should be clean all the way to its bottom, so the cable doesn't apply linear pressure or angular pressure. If you are working with the OEM cable, that square end can become slightly distorted or less than exactly square. It doesn't hurt to kiss it lightly with a fine file to get it closer to square. I have rotated them 90 degrees to find the best fit in a port that is also worn with age.
And about the dash illumination bulbs (4 of supplied by a orange wire), they operate through a dimming rheostat so there is going to be some voltage drop found there. And slightly above 13 volts is not a problem. Voltage regulator should allow 13.2 or so. Run the vehicle and maintain battery to just above 12 volts.