So, if I start CBR F4i with dimmer switch set to low beam, then all is fine, with lights working properly with both positions of switch. But, if I start bike when dimmer switch is set to high beam, then only right headlight works and only when switch set on high beam (ie when switch moved to low beam no headlight is lit). Not sure what could be causing this and would love to hear any theories...

 

Do both headlight bulbs (dip and main beam) work with the engine stopped? If so, it may be that with the engine running the vibration is affecting the switch which to me sounds to be faulty. Could be a faulty bulb(s) as well as the filaments may be connecting intermittently when the bike is running. Keep us informed as to how you get on?

 

If I turn the key to ignition (but bike off) headlights work properly only if at the moment I turned the key to ignition the dimmer switch set to low beam. In other words, lights work exactly with bike not running as they do with bike running, so I don't think it's a vibration issue, and the absolute consistency of it surprises me if it were just a bad switch (then I'd expect it to be more random but maybe I'm wrong in thinking that).