OK, I got my test light out and figured it out myself, so I'll post what I found:
Driver Side/Left Rear
Ground – All BROWN
Backup – YELLOW w/RED Stripe
Taillight – BROWN w/GRAY Stripe
Combo Stop/Turn – BLACK w/WHITE Stripe
Passenger Side/Right Rear
Ground – All BROWN
Backup – YELLOW w/ RED stripe
Taillight – GRAY w/GREEN Stripe
Combo Stop/Turn – BLACK w/ GREEN Stripe