1989 Dodge Caravan Intermediate loss of spark

Electrical problem
1989 Dodge Caravan 4 cyl Front Wheel Drive Automatic

I can get the vehical to start at times and it will run until I shut it off. At first it would drive and the engine would die and then it would run fine for a while and then not start. I replaced the distributer, coil, cap, rotor and Engine computer. No such luck, I was told it may be the wiring harness has a short, also was told that the oil pressure switch may be bad.
Like I said it gets fuel but no spark.