Moped Army

I have a 1978 Peugeot 103 with the coils inside the magneto.I got the bike running today and it runs and idles excellent until I apply the brakes then the engine dies.The headlight,tailight , brake light and the light switch all work fine.I installed new bulbs and swapped in new brakelight switches from a working 103.The brakelight bulb works and is not burned out, but like I stated earlier when I pull either brake handle then the engine cuts out.If I keep the rpm's tached up I can keep the engine running even when the brakelight is activated.All the lights and brakelight do work and work correctly but I guess something is shorting or /grounding out.How can I test and diagnose the lighting and ignitin coils? Also I have a wiring diagram from mopedriders .org but the wiring diagram is not the correct diagram for my application because the only wiring diagram that I could find is for a single rear tailight/brake light combo bulb and my bike has two seperate tail light and brakelight bulbs.Does anyone have the correct wiring diagram ( the two bulb type diagram for internal coils?).I have an audioble continuity tester and traced the tailight wires.The tailight that I have has four wires and looks like it is all factory wiring, the blue wire grounds to a bolt on the fender,there is a yellow wire which I guess is the switched 6volt feed,a black wire that goes to the magneto and a second black wire that that is grounded to the frame somewhere .Where should I start? How can I test the different compents while they are still on the bike? It would be nice to be able to check seperately the ignition coil ,light coil and condenser without having to unsolder and swap out out each component ! THANKS, PEUGEOT1