Starting Problems 1993 Cherokee

I have owned my 1993 Cherokee for just a year. It has high milage but the previous owner(s) gave it very good regular maint (as per sevice technician who now does the regular maint.) I have had periodic starting problems. I already replaced the the flywheel sensor on the bell-housing. That seemed to solve most of the problem. However on occasion I still have a prblem starting. Most of the time the engine turnes over but no spark or fuel pump not working... the problems have "traced" to relays in the main fuse box. After tapping on the box or the relays it will "wake up" and work just fine. I have even replaced the relays and checked for bad connections in the fuse block its self...The latest problem acted like a dead battery but we were able to once again tap on one or two relays and magically it starts... I have read about some of the same symptoms and some fairly exotic and EXPENSIVE repairs & have had most things ruled out by a service technician... The mystery goes on...
Any new ideas?