When we install a light or audio amplifiers in automotive, there are some things to consider  :

1. Make sure you use a cable rated for higher amperage, because if the value of small ampere results can be too hot and could melt the cable outlet and cause a fire. Beside that is likely to cause damage to the vehicle Where to Get Your Power

2. Many people would consider the hot wire into the existing circuits that use T-taps or connectors, specifically designed to entering the existing wire. This is not always a good idea for several reasons. First and foremost, the existing circuit into placing additional burdens on the circuit. Additional burden placed on the circuit or wire can exceed these limits cables, connectors and fuse will burn.
In most cases, the existing vehicle fuse blocks, cables and connectors are not rated to handle the additional burden of a high-powered off-road accessories such as lights and amplifiers. If you’re the type who likes to add all kinds of items for your vehicle may be feasible to install an additional fuse block that handles non-critical items like off-road lights, CB radios, power inverters, audio equipment, etc. This additional block can then be activated by a heavy duty wire able to carry the required current in the block all accessories. Be sure to fuse block in the battery.
Another important thing to consider is how you control the switching on / off of power to your accessories. In almost every case where high current is needed, the switch would you use to turn the power can not handle the load because most of the switches are not designed to handle higher amps. Power switching task better left to a relay. What is Relay? A relay is a device that, through magnetic induction coil, was the power to you. Switch installed in your cab 4×4 actually only powers the relay itself is very little current draw. In most installations 30 AMP relay from Radio Shack (Auto Relay Cat. No. 275-226) will do if your claim exceeds 30 amps amperes. I like to use the switch turned on in the cab to let me know if the driving lights on.