Adding a 12V outlet to your vehicle for powering 12V accessories is fairly simple and can normally be carried out in just an hour or so. The tools and the amount of time required depends on how and where the 12V outlet is installed.
It is normally possible to get power for a new 12V outlet from the vehicle fuse block. Other times it is necessary to wire a new 12V outlet directly to the vehicles 12 volt battery.
Direct wiring to the battery should also use an inline fuse holder and an appropriately sized fuse. The ground for the outlet should always go to the vehicle chassis.
You should also checkout our how to titled Adding a 12-Volt Accessories Outlet
Wiring directly to the 12 volt battery:
Begin by disconnecting the negative battery terminal from the vehicles 12 volt battery. The positive wire from the new 12V outlet will need to be fed/fished through the firewall. Normally feeding a wire through the firewall is relatively simple and should be done where wires already run through the firewall. Once the wire is fed through from inside the vehicle into the engine compartment an inline fuse holder should be crimped or soldered onto the end of the positive wire coming from the new 12V outlet. The fuse holder lead then gets a ring terminal crimped or soldered on and then attached to the positive 12 volt battery terminal. The negative wire from the new 12V outlet should then be connected to the vehicle chassis. Once a fuse is put into the fuse holder and the negative terminal reconnected to the battery, the new 12V outlet is ready to go.
Wiring to the fuse block:
Begin by disconnecting the negative battery terminal from the vehicles 12 volt battery. The fuse block inside the vehicle will most times have a few blank spots for adding your own fused line. In many cases the manufacturer will have also snapped in a few unused crimp ends. The crimp ends will be snapped into the fuse block but will have no wiring attached to them and will be located in an unmarked section of the fuse block. To attach a new 12V outlet to the fuse block you must remove two of the extra crimp terminals from the back-side of the fuse block. The first crimp end is either crimped or soldered onto the end of the positive wire from the 12V outlet. The second crimp end can either be connected with an appropriately sized wire directly to the battery, or by using a “wire tap” it can be connected to the main positive power wire feeding the fuse block.
Once both terminals are snapped back into the fuse block the new 12V outlet needs to have it’s negative wire connected to the chassis of the vehicle (the shorter the ground wire the better). Once the ground wire is connected a fuse should be placed into the new fuse block location feeding the new 12V outlet and then the negative battery terminal re-connected to the vehicle battery.