If there is an electrical outlet on the post (near the bottom -- 3-socket, female plug-in type I assume, in a weather-proof box) that outlet should be 'live' at all times for the lamp to have electrical supply also. You can test the SUPPLY of electricity to the whole lamp post by opening the utility box for the plug-in and pulgging a workshop lamp (or other safety-grounded portable light) into it and see if the light can be turned on. If not, there is NO electrical supply to the lamp post, and the trouble lies somewhere in the breaker box or in the underground electrical cable from the breaker box out to the pole.
