wiring M3 style mirrors

I'm going to be doing a set of M3 style mirrors soon (the ones with the signal light on the front of the mirror like BMW's).  I've never needed dedicated left and right blinker signal before...so I'm thinking about where I can grab it easily.  I was thinking right at each marker under the hood...run a signal from each marker element, and use relays to trigger the mirrors.

Is there an easily identifyable set of wires under the dash that will provide the same signal?  Its a 1994 Ford Ranger...I haven't seen the mirrors yet, so I don't know if they have both signal and parklamp elements, or just signals....parklamp signal is easy enough to steal, but where can I find dedicated right / left blinker signal??

thks.

b