If you have not found your problem, I may have. I have (had) the same issue. I thought it was the circuit breaker, I have a new one on order. But in the mean time I found this: http://www.agtta.com/Tech-Tips/Tech-tip-ZW-repairs3.pdf
Check out page 3. It talks about a bad resister wire. I did what they suggested, swapping out a 14 volt (I had no 18v bulbs) and running a jumper wire where the resister wire is at. All of a sudden my red light worked when I shorted out the system. I'm still putting in the modern circuit breaker when it gets here as I felt it took a little long before it tripped, but it did trip and it did light up the red light. Now I have to find 18v lights with the little globe as the ones I have are too big to fit in the red light dome.