Strange Problem

I have recently finished a resto on a 6 volt ST70. She runs well but with one strange glitch. The main headlight and rear light will only operate with the engine running! Switch it off... nothing. The battery, loom and rectifier have all been replaced. I am not really too concerned as the light output is pretty dismal, and the thought of riding at night does not appeal. However this snag may mean problems with an MOT which would be a shame. Any thoughts?
Regards, Pete.

Please look at earlier postings relating to this issue and it will confirm that this is normal only the brake light and horn work without the engine running
Regards Tufty