Have checked plug wire, coil and still no fire on one side???

What bike? Points or electronic ignition. If it has points and you open, then close the points the plug should fire. If not check the wire from the points to the coil(Ohm meter) If wire is good, check to make sure you have power to the coil on other wire to coil. If power supply is good and ground is good, you have a bad coil or possibly condensor. Most likely coil. Make sure there is nothing between points causing them not to ground.(Ohm meter or take points wire directly from coil to ground) Each time you ground the coil plug should fire.

Sorry about the lack of info// 850 73 with branson electronic ign have swapped the wires and coils back and forth to omit that, so I take it must be in the wiring harness. was hoping it was a part I could replace, ya know.. tks

With the Boyer ignition both coils fire at the same time (Wasted spark for one) so if one coil is firing, they should both fire. If you switch the wire from the ignition to the coils the other coil should fire. This would mean a wiring problem. (On Boyer usually at the solder point on the distributor board) If not we are back to a coil problem. Check for negative power to coil, maybe switch condensors. Not sure how you are checking for spark? Timing light or externaly grounded spark plug are the easiest way. If you are going by how the engine sounds running it could be other problems. Would need more info/ what you have tried, to tell you exactly where your problem is.

Thanks for the very god response... next step is to try and check t see if in fact the coils are good or not, and like you say maybe the condenser, since this problem, I pulled both coils and checked the connections, and refit everything and now it won't start at all and seem to have no spark on either side. Good british electrics... thanks again and will try this wknd, maybe next step is new coils, and is there a way to ck if the condenser is bad?

I had the same problem. Turned out the plug was cracked inside ,very hard to see. New plug - No Problem. Maybe you'll get lucky too!