I added a side door lock button to my '03 EB----they already come with one in the rear doors.

Being **** as I am I used Ford OEM parts, switch and pig tail connector cost about $60 for the pair. From there its simply a matter of mounting the switch and connecting it in parallel with the existing PDL circuit. I fabricated my own ersatz wiring harness, ran the wiring inside the nearest roof rib which isn't a feat for the weak or lazy.