The All-4 harness is a great way to increase light output on dark roads. The harness includes a relay circuit to keep the low beams on while the high beams are on. By default, from the factory, the low beams turn off when the high beams are activated. This harness will eliminate that feature for some insane light output which is only magnified with an HID conversion kit and/or high-powered LED's.
Installation is a piece of cake and is all done in the under-hood fuse box. The only needed tools are a 10mm and 1/2" nut driver (or similar tool). This modification (like most others offered) is 100% reversible with no trail left.
Please keep other drivers in mind when using this insane light output modification. High beams are naturally aimed higher and will likely impair any oncoming drivers vision.