Thanks I got it sorted out. There were 2 short wires coming out of the headlight to be connected to longer wires to the taillight, and the polarity the wires at the headlight wasn't obvious. Took a guess as to polarity, connected it up, and it worked.
No obvious grounding points anywhere (these are modern lights).
Originally Posted by
steelbikeguy
is the ground wire on the tail light connected to the ground wire on the headlight and/or dynamo?
Sometimes B&M (and other manufacturers) connect one of the mounting bolts to one of the electrical connections. The same might be true of the headlight and dynamo. The idea is to make it easy to use the frame as one of the electrical conductors, and there may be some sort of ground symbol next to the bolt or electrical connection.
If the same wire doesn't go to the grounded electrical contacts at each end, it is possible to have the effect of allowing the current to flow around the tail light instead of through it.
a quick, lousy illustration of this issue....
Steve in Peoria