Small Engines (Lawn Mowers, etc.): Deere no-start: Cud be relay or safety interlock?, army signal, starter relay

Question
Have a Deere Sabre Lawn tractor, mdl 17.542HS. Won't start suddenly.  Cranked and worked fine.  Shut it down, then about 20 mins later it won't start.  Made sure but was in seat, brake was on, and PTO for blades was disengaged.  Still no starter movement at all .  Dead quiet. Ignition switch turns to first detent and turns on lights fine. Go to next detent and dead quiet.  No click of starter relay....nuthin.  Pulled battery and replace with new one.  No chg.  Pulled seat safety interlock swict and cleaned all contacts and still no hit to the relay.  Checked brake safety interlock switch visually and it is deperessed when brake is engaged.  I believe it is either: starter relay, PTO safety interlock, brake interlock, or seat interlock.  Any ideas on this and how to test to narrow it down?  BTW, am old Army signal guy.  Never liked working radios in tanks.  Always afraid a spark would light-up the hydraulics in the turret.  Thx for any assist, RG in MD.

Answer
On my first trip down the table 8 range as a tank commander our dome light wire came off and started arcing aqainst the hoeycomb.  Now that will scare the crap out of you.  We all jumped out and ran and let the engineers fix it.

Now for your question.  The seat switch means nothing. forget about it.  Get out your test light.  Start at the ignition switch and find the wire that flashes when you turn the key to start.  The circuit goes from the key switch to the pto switch to the brake switch to the solenoid.  Where the current stops is where the problem lies.  Usually the brake switch or the solenoid itself.  All of the wires will be purple.