A word of warning - before you start tying trailer lights into your
car's brake/running/turn signal circuit, make sure your vehicle
doesn't have a computer connected to the lighting circuit. A clue of
the use of a computer is that you get a message on the dash when a
brake/running/turn signal light is out. If such a computer is being
used, you can blow it out if you draw too many amps.

Here's a link to a previous RAS discussion on trailer light wiring
that relates to the current topic: http://tinyurl.com/6kf9ab

-John