Use this if you need to install and extra aftermarket electrical component. See video below.
HUse this wiring adapter Kent designed to connect to one of the fuse posts in your fuse box to give you a "keyed" on-and-off power source for an electrical component you wish to install. The video below will give you more details.
W116 W123 W126 Keyed Power Source Wiring Adapter to Fuse Box
$18.50
SKU:
COM-KEYEDWIRE 
Product Details
If you need to use a relay to power a high amp draw component here is how this would help. Connect this to a keyed power source in the fuse box. Connect one open hole in the Wago connector to a switch and then connect the switch to the switch wire on the power relay.
