Most 6V/3W sets use a 2.5W front bulb and a .5W rear bulb; the headlight gets most of the juice. If the front burns out the rear will blow almost immediately from the resulting overload. To test just the generator with a meter I'd connect the + probe to the point where the wires normally connect and the - probe to the bracket of the generator (its ground when connected to the bike frame). Spinning the generator by hand might not give enough ooomph to provide output so you might need to hold it against a turning tire. Good luck!