Nissan Repair: 94 pathfinder starts intermittently, aerospace engineer, starter wire

Question
I have a 1994 Pathfinder that starts intermittently.  When I turn the key I can hear a single click come from under the car.  If I turn the car off and do it again its the same noise.  If I turn the key very rapidly it usually starts within about 30 turns of the key.  I replaced the starter and it worked fine for about a month.  After that it started to act up again so I thought maybe I got a bad starter.  I changed the starter again but it still only started maybe every other time.  At the beginning of this whole thing about 2 years ago I had to just hold the key in the on start position for about 5 seconds and then the starter would engage.  After a while it became ten seconds, and now it only seems to work with the rapid turns of the key.  One time I tried for 2 hours (no kidding) and it still didn't start.  My guess was the ingnition switch, maybe bad contacts.  I have tried going up and down the gears like I've read in other answers to problems presented to you but it doesnt work on the first or second tries.  It has 4wd and its automatic.  Any ideas before a spend $120 on a now ignition switch would be greatly appreciated.  
Thanks, Mike.
P.S.  Are you an engineer who worked on the Raptor or are you a pilot? and where did you learn so much about nissans?

Answer
Mike,

First, I would get under the truck with a test light and have someone turn the key to see if it is getting current to the starter wire.  This is the small wire that connects to the starter.  If there is no contact then I would do the same thing under the dash with the large wire that comes out of the ignition harness.  There are two, one is power coming from the battery and the other one goes to the starter when the key is turned.  Use a test light and probe.  If the wire is hot all the time it is the power wire.  The other one will be switched ignition.  If there is power from the key then I would replace the relay.  

I worked as an aerospace engineer on the Raptor and miss it really bad.  Currently, I am a manager at the Department of Energy working in Nuclear Technologies.  Oh, I am a car nut and have had over a hundred cars in my time.  That was the nice thing about the Skunk Works...  If we were not working on aircraft we were working on hotrods.  Curently, I have three Nissan's and have had many in the past.  Oh, I worked my way through college working at a Chevy dealership...  I am a pilot but have not flown the F/A-22 Raptor.