Join Date: Mar 2010
Location: Miami, FL
Bikes: 08 Giant OCR C2, 05 Specalized Hardrock Sport Disk
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Start by checking for continuity. You can do this with a multi-meter. You do not need an expensive one, $10-$15 will get you what you need.
Check continuity from one positive connector to the other. If you get a good reading, check the ground side.
If the continuity test is good, check out the connections on the light housing.
If that is ok, then the generator might be bad. The multi-meter can do a load test up to 10 amps, plenty for a bike dynamo. Get a buddy to crank the pedals, while you test the output voltage / amps.