Why 10.7 volt input at ‘71 Duster instrument panel?

RedFish said
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 an 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.

I just looked at cable routing with cluster removed and it appears to be coming in pretty straight. No better option. I inspected the end of the cable and it looks clean and smooth. I looked at the head of the speedometer and see nothing unusual there. I repeated the speedo check with the electric drill and, again, it runs smoothly on the bench. I don’t know where the speedometer cable was made - I just wrote the seller and asked. The picture of the cable end shows that the flex cable is almost flush with the plastic head - which the speedometer shop tells me is the correct position. The second image shows my eBay receipt. Would the price suggest that I didn’t get a good enough cable?