UPDATE
Dear All, thank you for replying. Very helpful information in there. I have taken more photos as requested. Some answers to the questions, in order of comments.
I tried to draw a wiring diagram but I am plain rubbish at doing it. The basic wiring is from the AXA headlight one set of wires goes to the Dynamo hub - which works. The other set are connected to another extension wire that runs to the back of the bike.
I can't find a switch anywhere. The bulb is definitely new.
The light might be an older generation, but it is brand new.
The light is an AXA Pico 30T Steady. I have included a screenshot of the spec sheet.
First timer, learning a new skill. Please forgive any newbie mistakes. I am truly learning step-by-step. I am building my first bike ever from scratch. Well, I found a destroyed bike on the street and broke it down to the frame and built it back step by step to learn how a bike works.
The Dynamo hub in the front wheel is working well, and the headlight I installed is shining nicely.
However, here is where I am getting lost. I have hooked up the rear dynamo to the rear rack, and installed the cable from the front dynamo to the rear.
I can't get the rear light to work for the life of me, and need some advice on how to diagnose the problem.
I am using a multimeter and getting a signal out of one of the leads from the front Dynamo, and the cabling is new (everything is brand new), but the rear cable leads are not registering anything.
I have included a picture of the rear dynamo (Busch + Muller Toplight) in case anyone says "How could you not KNOW you need to do such and such...).
Anyways, I read the posts on Dynamo problems which seems to deal with hub problems. My front light is burning bright, so I'm pounding my head against the wall.
Any advice would be much appreciated.