You shouldn't have to worry about the car's electrical system. The tiny amount of extra current won't even be noticed.
You do want some kind of fuse for the lights. That fuse doesn't protect the lights. It protects the wire if one of them rubs through and shorts to the body. There's two acceptable ways to fuse what you add on. You can connect a wire anywhere there's 12 volts then run straight to a fuse holder you add. In fact, many accessories like lights and radios come with those fuses already wired to the products. If you have to run to the auto parts store and buy a fuse holder, the better way is to just connect it to an existing circuit that already has a fuse in it. (Think of your bed room with all the lights on one circuit breaker, and you add another table lamp. It will be running on the same circuit breaker. You're doing the same thing on your car.
I made this sad drawing to possibly explain it better. This shows the battery on the left and the fuse box on the right with three fuses shown. The bottom one has been removed. Probe the two terminals in the socket with a test light or voltmeter. The terminal on the left, with the blue arrow, is connected directly to the battery and the test light lights up. You want the other terminal on the right where the test light does not light up. That is the side where everything that comes after it is protected by the fuse. Attach your light's wire by the red arrow.
Some wires have 12 volts all the time like what I drew in my picture. Some only have 12 volts when the ignition switch is turned on. You get to decide which one to use. Do you want to be able to turn the lights on anytime or just when the ignition switch is on?
There may be some single-terminal taps in your fuse box inside the car that already have 12 volts all the time of after the ignition switch. Those are often fused with a really large fuse under the hood that feeds many circuits. Chrysler, for example, uses a lot of 40 amp fuses that feed a bunch of smaller fuses, one for each circuit. If your light's wire rubbed through on a sharp edge of a metal bracket and grounded out, it might be too thin to pass 40 amps, so the wire would still burn up and the 40 amp fuse would not blow. In that case you'd want to add a smaller fuse to protect that wire.
Wednesday, February 20th, 2013 AT 3:31 AM