Nissan Repair: 95 Pathfinder starting problems, pathfinder, crank

Question
My wife's 2WD AT Pathfinder recently developed a starting problem.  The car was power on, but wouldn't crank.  This was intermittent.  The mechanic replaced the starter and I thought all was well, but not more than a week later, the truck decided not to start.  I've heard that there is a relay inbetween the battery and starter.  Is this true?  If so, could this be a source of the problem?  If it might be, where exactly is this so I can replace it?

Answer
The starter sounds like it is fine and it may be the contacts in the ignition switch.  First I would check to see that the battery is charged fully and that all the wires are tight.  Lastly, I would check to make sure the starter interlock is not going out.  When you start the truck try starting it in neutral instead of park and see if the truck will start.  Now, while you are turning the key move the shifter back and forth with your foot on the brake.  If it is a manual push up and down with the clutch.  One of these switches may be defective and going out.