I know from my 907, that when i fit dual headlight with 2 x 55W on, it start to drain current from battery, what causes such thing, that cant start anymore hot engine after driven 1 hour! BUT to my bike didnt happen any failure to regulator, or to generator, only too much current from battery, cause generators have to do very hard job in 907, caused by injection... 907 have too small generator. I solved that problem to add one switch to light system, that no need to use hole time both 55W bulbs, only, when really needeed... I have added also 2 realys for helping low and high beam currents, but that is totally another thing, nothing connect to this "generator problem".

Anyway i think, that 750 Paso use only small amount of current(carbied engine), so You have to check Your system, where is that problem...... I quess, that You only loose that generator from old age, if Your regulator is ok?