MSC09809 Boss Headlight Adapter Kit 2003+ GM C4500 C5500

Boss Plow Headlight Relay Kit # MSC09809.

This kit is for a 2003+ GM C4500/C5500 This has a 5 pin oval plug to adapt to the truck. 

Here is a link to the Installation Instructions. 

To make sure this is what you need for your truck, check Boss' Power Match.