Eric, I don't have a Painless harness so this may not apply, but here's a thought. The front lights have three wires, a ground, a red wire for running lights and green for turn signals. On the stock Mustang harness, the power source for turn signals is different than for running lights. I would think this would be true for the Painless as well. Since the power sources are different, the fact that the turn signals work doesn't mean that you have power for running lights. I would check the power source and wiring of the running lights. Good luck!
Galt