BACK UP LITES

My b u lights are inop i have a 1998 legacy outback wagon 2.5i manual trans. 1. The bulbs are ok 2. The back up switch is ok 3. The fuse is ok the indication is the lights come on then go off immediately. I have done the following checks: Disconnected the switch pigtail and shunted across the plug ends to the lights. The indication is the same, on then off. Please advise if there is a relay in the circuit and where it might be, or something i have not already checked.