Okay so I bought a new starter about a year ago and installed it everything went well but a couple times i went to start her up (my 1991 jeep xj 4.0 straight 6) and the starter would grind, id try again and it'd fire right up. Then a couple months later (now lol) I turn the key to the start position and nothing, the fuel pump whirls, starter relay under hood clicks, all connections look well, I replaced the ignition switch (box under the steering column not the cylinder) and i can feel the actuator rod move to start position. and still no start. I volt metered the wires on the starter. The red has 12v but the ignition switch wire has no power when tried to start. what else do i do? I mean i can recheck to see if the actuator rod isnt all the way engaging start, ive replaces the relay now... still nothing. could it be the solenoid?

 

91 is Chrysler system not Renix? (I never remember the changeover year)
If so, the start relay in the PDC is the next place to look. See that you have power to the relay contacts and that the relay operates when you turn the key to start. CCKen posted some good diagrams of this in another thread

 

Automatic maybe NSS issue...