mtushmoo

The six pin for the '16 and up harness with both Stop Light and Cargo light wires is back in stock on Amazon: https://www.amazon.com/dp/B07C488SBN The 8 pin harness is available on ebay. User mtushmoo

The six way connectors are back up on Amazon. I have the 8 pin version available. user mtushmoo on ebay.

https://www.gmupfitter.com/files/media/photo/920/UI Bulletin_122b.pdf According to GM, the change occurred between 2015 and 2016.

It uses the connector that the bed lights are currently using. It provides a ground wire, a third brake light wire, and the cargo light feed that works off the dash switch with the same functionality as the factory bed lights. If you have the bed lights and want to add a third brake light you can track down the terminal and seal and add the wire to the connector body you have, or get this connector and splice the bed lights on to it.

The connector for the lights is on Amazon. https://www.amazon.com/Silverado-Connector-Harness-23295942-23327843/dp/B07C488SBN

The connector is on amazon. https://www.amazon.com/Silverado-Connector-Harness-23295942-23327843/dp/B07C488SBN/ref=sr_1_9?ie=UTF8&qid=1530099338&sr=8-9&keywords=silverado+chmsl

The '16 and up harness with both Stop Light and Cargo light wires is on Amazon: https://www.amazon.com/dp/B07C488SBN $30