Originally Posted by gsa103

There is a solution but you're not going to like it. Get a new bike computer with ANT+. Its a digital wireless link and dramatically more immune to RF noise.

The problem is that non-digital cycling computers use the dumbest possible RF transmission scheme, basically just emitting an RF pulses as the wheel spins by. Many lights use DC-DC switching converters for power control of the LED. These switching converters are extremely efficient and typically operate at in the same RF frequency range as the wireless computers.

You can try shielding the battery wire by putting conductive wire mesh loom around the cable. It might get you enough. In general, shielding on a bike is tricky since you don't have access to a good ground.