I got time this AM to spend some time with my DVOM on a 2000 C7500 3126. There are only 5 pins used out of 16. PIN 16 same as all OBDII style connectors is constant B+, pin 4 is ground, turned key on, pin 7 to pin 15 2.2 2.7 volts, pin 6 to pin 4 B+, pin 6 to ... Login to read more.