1995 Chevy Suburban Low voltage

I had a 3 year old battery that was leaking acid. I replaced it. 3 weeks later I noticed when starting the truck one day it just made a clicking sound but when I cycled the ignition switch, it started. It did it again about a week later, but again started after a second try.
A week after that it just went click. The battery indicates 12.66 volts, but the voltmeter on the dash shows about 9.5. The headlights are bright, all the elec accessories work well. There are 3 wires coming off the positive side of the battery. Which one does the dash voltmeter read from? If it reads from the cable that runs the starter that would make sense that everything is getting power from the batt except the starter.