Electrical problems

Hello guys, maybe someone can give me a tip. Drive for about 20 years a 92 Zephyr1100. I have now almost 140,000 km on the clock, since then actually almost without problems. But recently the mill starts to annoy. Starts right after the first push of a button and runs quite round, even if it is cold. But sometimes – not always – so about 100-200 meters after the start, the revometer goes abruptly to zero and the cart stands. And that with beautiful like in bad weather. If I’m lucky then she jumps back and forth after several ignition keys and violent cursing again. I have changed almost all switches meanwhile, clutch switch, side stand switch, right handlebar fitting and even the lower part of the ignition lock with the electrics on it, but the problem comes again and again. I checked the battery cables and they are fixed. Recently she even goes during the ride on the fast road. ßeße – and that’s not very fun, if you are just overtaking. I cleaned all plug connections and treated them with contact spray, but the problem still occurs again and again. Maybe someone has the same problem. For a good advice I would be very grateful. I don’t want another mopped, because I don’t like any other as well as the Zephyr.