Suzuki GS750 only firing on two cylinders?

i have a 1977 Suzuki GS750 thats only firing on cylinders 1&4 carburator and intake are ok new spark plugs ignition coils seem to have continuity there is a modification in the contact breaker it is called Marlek 440 and it has three wires coming out of it it is sealed i have a '76 also and the contact breaker has only two wires do you know where the third wire goes? the previous owner had modified it for saddle bag indicator lights and the wirings pretty messed back there also the battery wont hold a charge this bike obviously hasn't been driven for a while although it did fire up ok only on the left side