Mix brown sugar, ketchup, soy sauce, broth, ginger and garlic in a small bowl. Take out 1 cup and reserve for basting (and refrigerate).
Place the rest of the marinade into a large Ziploc bag with the thighs. Refrigerate overnight.
Discard marinade from chicken and grill thighs until no longer pink (about 8 minutes per side), basting with the extra marinade as you grill. Serve warm. ENJOY!