Motorcycle Repair: Electrical/Idling problem, ok coral, voltage test

Question
QUESTION: 1985 FLT  Evo  Problem: Starts fine, runs awesome, when dry and no lights are used. It seems when i turn on all the lights the rpms drop really low and it will stall, if i giver a little gas she stays running. No lights, she runs great!  The more juice I draw the lower the idle. With all the light's on it seems to drop about 500 rpm? Tonite was worse, pouring rain, backfiring like crazy, seemed like the ok coral was in town!!Where do I start to look? Could these these two issues be related? Possibly all moisture related? The bike is now in the warm and dry in the garage and seems to run fine other than the lighting dropping the RPM's?
Thanks

ANSWER: Check at the battery, with a volt meter, and let me know what the voltage is with the lights off and then the lights off.
Mike

---------- FOLLOW-UP ----------

QUESTION: -Before starting bike, 12.6 volts
-Idling for warm up, 14.6V was measured
-Normal Idle at about 800 RPM 14.6V
-Any lighting turned on, in no particular order Headlight, or tear drops, RPMS drop to about 500RPM, 12.1Volts measured
-All light back off RPMS stay low, have to crack throttle to get the rpm back to normal.
-Turn the lights back on, Voltage drops to 12.1 and RPMS to 500
-Start to crank throttle voltage is 12.9V at 1000RPM
-At about 1500 RPM we are back to 14.6V

Thanks


Answer
It sounds like the lighting is robbing the ignition of voltage causing the bike to stall. I would do a voltage test on the stator and see what its putting out. You can test it by using a ac volt meter at the stator wires. let me know what it is at idle and at around 1500 RPMs
Mike