Is that a Rough Country/Cree light bar switch? As others have said, you just need to grab
ACCY (Key-On) power and then run the light bar through a relay that's controlled by the Key-On power. You'll want to use a relay because the ACCY circuit is shared with other items and is limited current. For a standard automotive relay, the wiring would be as follows:
- remove the light bar positive connection and connect it to 87
- connect the battery to 30
- connect ground and key-on accy power to 86 and 87 (either way)
- (If the relay has am 87a terminal , it will not be used)
A detailed write up about relays with lots of pictures can be found
at this page, if you're looking for more info.