1982 RR doing very strange things

my 1982 RR is lpg converted but this happnes on petrol and gas .......
runs like a dream until i put the headlights on then stalls when i stop tuen headlights off ticks over fine have tightend the fanbelt but still stalls with head lights on please help

Russ

May be way out here but could it be a poor earth or other wiring fault? I'm no expert on wiring (I can rewire anything just don't pay me hourly or expect me to understand where all those electrons go! Know I've gone through several light switches (until I 'relayed' everything) and it may be on same circuit as ignition (possible ignition switch fault?) - If you have a multi-meter and a little knowledge, bypass ignition switch and light switches with "Heath-Robinson" wiring (easy with a little thought, a pen&paper (draw circuits) and a spare day).
Poor earth should stop engine starting, goosed regulator will affect chargelight coming on and will let battery go flat without you knowing but as you haven'tmentioned start probs this is unlikely. If all else fails, try removing steering column plastic-cover thing and flicking light switch/ ignition in the dark (night-time seemsto be best ) to see if any shorts are visible. If none of this works,please post what you have done/tried to allow people to eliminate causes. Worth doing anyway- visit your local motor factorand get him to make up two new earth cables - one to go from engine to chassis,and one from battery to engine - this always helps(even from a 'peaceof mind' POV) andclean faces before fitting.
HTH