How to check your dynamo system?
When checking a Dynamo system, there are 3 basic items which need confirmation:


Power Supply: Is your dynamo producing power? Checking this requires a multimeter, preferably with alligator clips on the wiring, and to spin the hub. Or there are specific tools, as well. 
Wiring continuity: Are all connections tight? Are there any breaks/shorts in the circuit? This can also be checked with a multimeter. It is best done by isolating each section of the circuit to check, and then verifying the connections between the sections. 
Light Source: Last, check your light source. Change the bulb if possible. Use an alternative 6v power supply to check whether the light head is functional or if there is an issue elsewhere in the loop. 


Busch &amp; Muller make a rather expensive tool for troubleshooting a dynamo.