I'm having a similar problem with my 90 4x4 Cherokee. Turned it off the other day and when I went to start it a few minutes later I got auxiliary power but no crank at all. Tried to jump start and still nothing so I tried jigglin the shifter and checked that my reverse lights do come on assuming a NSS problem with no luck. I Beat the starter up a little bit still with no luck. I was able to get it started by jumping the starter so I assumed it was an easy fix of replacing the starter but god knows mornings easy. Starter replaced with exact same problem. I checked all the connections to find a wire lose from what I believe is another starter solenoid to the left of the engine? Plugged it back in and started right up so I put my old starter in to return the new one and now it just makes a single clicking noise (coming from the starter) but won't actually crank. Naturally I put the new starter back in just to have the same problem. Still starts when I jump the starter directly... FML. Any ideas?

 

bad connection were other selinoid is you found is