The current setup is magneto coil earthed to bike frame and output to silicon half wave rectifier which charges battery and supplies lights etc. Simple I thought, take the coil output, connect input to bridge rectifier, conect other rectifier input to bike frame. Now I have full wave rectified output which gives me over 12v when smoothed! So now I connect the -ve output of the rectifier to earyh (bike frame) BUT I ger sparking and the voltage drops to around 5v. It appears the output is then +6v at +ve and -6v at -ve. Someone suggested isolate the AC alternator coil from ground then rectify and THEN connect the negative to earth. But its hard to modify the coil. Any suggestions please! See picture of circuit