How to select a power transistor to protect old school automotive ignition and headlamp switches
There are many 'High-side switch' IC's available for this purpose. Check the application notes for details on how to use them. But as mentioned by smashtastic, check that the vehicle is negative grounded.

The wetting current can be provided by bridging the two contacts with a capacitor (from http://en.wikipedia.org/wiki/Wetting_current).