This is a very simple tutorial how to make your Wii car-compatible.
Step 1: Making a Fitting Power Supply
Step 2: (recommended) Softmodding Your Wii
If you want to hack it ask Google for "Wii Homebrew". You can choose all games from USB and do not need to change discs while driving.
Step 3: Making an Adaptor "Wii to Car Monitor"
Step 4: (optional) Making a Sensor Bar Into the Monitor
In this step we need soldering equipment.
Screw up your monitor (1). Then drill 2 holes in the upper or lower part. Put in there IR leds (2). Connect these to a voltage regulator (3). Connect this Construction to your power input (4). Finally you should have IR leds which are working without any specian Wii cable for the sensor bar.