Bit of a silly question but am not with my bike so cannot check. I understand there are two bulbs in the rear light unit. One bulb works normally, however the other does not illuminate *unless* I'm braking. Ie it's not working as a tail light bulb, only as a brake light bulb. Those bulbs seem a bugger to access - just a case of changing the bulb or is there a loose connection? I need the bike for a 100mile comute everyday so advice appreciated!