Hi, as the rear brake operates so does the rear brake light, so that rules out faulty bulb and wiring up to the point where the front brake light switch wiring connects to it. Have a look around the pivot area of the front brake lever & you should find possibly a plunger type elec. switch with wires coming from it, now look at that part of the lever that touches this plunger should be some type of adjuster usually a lock-nut & bolt, adjust this in/out until the rear light comes on. It could be a faulty switch/wiring/connections if the adjuster doesn't do it.
Ted
March 2011
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