Wipers don’t work on high. 2005 chevy 2500hd

[PeterArbic]

All the wiper washer functions except the wiper high position work fine . Blue / white wire and yellow wire  from wiper module shows 12v at combination switch plug  with key on . Where does the ground for the blue wire ( wiper high) exit the combo switch so I can test continuity through the switch when switched to high position and so I can trace it from switch to ground. Any other diagnostic tips n how to test the switch or a pin out of combo switch much appreciated Cheers...Peter