Softbrake. I also bought their solid (no top light) tombstone housing. I bought the cheapest lighted license plate frame I could find on JPCycles.com and ran the wiring into the brake light housing. I grounded the ground on one of the bolts inside the housing and ran the positive wire to the tail light bulb itself. I just wedged the exposed wire in between the bulb and the receptacle. 10K miles and it still works flawlessly. HTH.
Housing = J&P #340-755
Plate bracket = J&P #340-750
Plate frame = J&P #340-460
Don't know of a Harley equivalent...