First check the starter interrupt relay (for the anti-theft)
Either swap it with another or just jump the #30 and #87 pins on the relay base.
If it now cranks, it's the relay, wiring to it or the anti-theft system has a fault.
If still no go, hook up a multi-meter to the starter solenoid turn-on terminal and ground. Turn the ignition to start. If you have B+ at the terminal, bad connection or bum starter or solenoid. A tap with a hammer will typically get it going TEMPORARILY. Make sure connection is clean and solid. 96+ typically are ok but -95 modulars had a cruddy spade temrinal here which gets corroded and such.
If no voltage at solenoid turn on w/ ignition on START, do the same test but at the MLPS (R/LB wire for starter in, W/PK out)
If voltage going into the MLPS with ignition on START but none out, bad MLPS (which also functions as the neutral safety switch)
If voltage in and out, there is a wiring issue between MLPS and starter solenoid.
Let me know if you'd like a diagram