Yes, the black wire on the Curt T-Connector Vehicle Wiring Harness part # C55562 which is a fit for a 2005 Dodge Magnum will need to be run to the vehicle's positive battery post with a fuse in between. The extra wire, fuse, fuse holder, and wire connectors that you will need for this are all included with the kit for you. view full answer...
The reason you want to run the power wire all the way up to battery is so that you bypass all of the delicate wiring of your vehicle. The power wire is required on trailer wiring harnesses for some vehicles because the electrical system on those vehicles cannot handle the amperage draw associated with trailer lights. Powering the converter box with a power source that doesn't come from the battery would defeat the purpose.
I attached an FAQ article on routing the power wire for you to... view full answer...