How to ground PDC?

Mike69cuda said
Since it is plastic, it would have to ground through the harness. There is no case ground.

Looks like Del & I are simultaneously posting again. I am in great company!

Yes Del is always a great help! I have the harness grounded to the firewall but am now questioning if the stock vehicle had harness grounded to back of head. Would this make a big difference? My sensors are not happy :(