[Jon Stratis]

Peter, lets go back to the beginning here, because I'm suspecting more and more the fuse Al mentioned, and a short somewhere in your wiring. If, for example, you wired up the signal light incorrectly, such that it permitted such a short, and successively tried all 4 side cars with this same wiring, it's possible you blew the fuse in all 4 side cars. Even if you had fixed it (the second signal light you tried), because they were already blown it wouldn't help.

Where is your team located? It could be handy to have another team nearby assist with some debugging. For example, if their signal light works, you could try replacing their side car with yours - if the light now doesn't work, then the problem is in the side car. If the light does work, then we know the side car is not the issue and can start tracing it back from there.