Electrical problems

1989 ford ranger with a bazillion miles on it. Four cylinder with 5 speed. Started missing really bad intermittently and got worse as time went on. Carried it to the shop and had the cam sensor replaced. (Crank sensor??) All was well for a little while but then same thing so I carried it back. The head mechanic says he can’t find out the problem. Seems to be a wiring issue (short). He says it misses when he wiggles some of the wiring but not anything reliable. Some times it will, sometimes it wont. He also said that he can turn the ignition switch past the on position and it helps…sometimes, but not all. All other electrical components have been replaced. He also said he had another ford ranger there with the identical problem and can;t figure it out either. Does anyone know of problems with the rangers??