Number one, make sure you use wire that is rated for the amperage that the accessories is going to pull. It is always better to have wire that is OVER rated rather than wire that is not rated high enough. If wire is used that is not rated to handle the current that your accessory will pull, the result could be overheated wires that could melt the insulation, causing a short or worse yet it could result in a fire. If you know how much current your accessory will draw you can determine what gauge wire is appropriate for your application.
Most wire in a vehicle, if shorted out, will burn up before the battery overheats and possibly explodes. If wire that is over-rated for vehicle use is used and a short occurs, a short will most likely result in damage to the vehicle of some sort unless a fuse is put in line as close to the battery as possible. With the fuse there, in the case of a dead short, the fuse will burn out first before any damage could occur.
The method I use for wiring the lights and other external accessories, for the most part, follows the diagram pictured above. As in the diagram a wire is run from a 12 volt power source to the switch in the cab and out to the relay placing a fuse at the source of the power. (Follow the relay’s wiring schematic when connecting the wires to the relay) One of the relays terminals goes to ground.
