Simple (?) addition to a driver circuit?

[thomas.hood]

Hello All,

I asked this over in the bicycle lighting sub-forum ( http://www.candlepowerforums.com/vb/showthread.php?p=2665382 ) but got no responses, so seeing as it's a generic circuitry problem I thought I'd ask here.

I've got a PCB for a circuit that drives a string of 3 white Crees from a bicycle dyno. What I'd like to do is make an addition to the circuit such that instead of powering this string of 3 Crees continuously, the output would be switched back and forth between the 3 whites and another string of 4 reds (~Vf to 3 whites) at the rear of my bike. I.e. the strings would 'flash' alternately.

Any ideas how this would be best (most simply) achieved?

Thanks,

Thomas Hood