If you had a Clymer manual and could look at the schematics, you would see that the lockouts are controlled by signals from the reverse controller and the ECU. We have given you what signals influence the lockouts to test.
1. Kill switch ( power to emergency shut off)
2. Gear selector ( not in neutral with stand down kills emergency relay, clutch must be in to start)
3. Side stand switch ( down while in gear kills emergency relay)
4. Clutch lever switch ( in gear with leaver not in kills starter relay)
5. Reverse switches ( Starter relay is connected through them)
All of these either disable the emergency shut relay or in the case of the clutch switch, the starter relay. They are safety lockouts so prevent starting unless certain conditions are met. They all go through the reverse controller. It is a good first step if you verified all the other pieces.
Your ECU looks perfect but the it turns on the fuel pump, runs all the injectors and the coils, has the input from the throttle so if the ignition was turned on with the backwards battery, unlike the always hot links to the reverse and ABS controller, it could have also damaged that but we won't know until you get that far.
In addition to Gordon's list above, when troubleshooting these type of problems, IT IS VERY IMPORTANT to remember these points:
1) If one does attempt to set / check his hall-effect-sensor (ignition trigger) using GS911, you may leave the ECU in an unknown state when the whole GS911 procedure is not completed until the end. In such unknown state, the starter will turn but engine will not start.
2) Normally, when all is well, after you turn ignition ON (just before attempt starting), the RED engine-temp warning-light should go and stay ON (until engine starts). In same logic, the fuel-pump will prime as it is connected to ECU via Hall effect sensor trigger - all these being related to starter interlock conditions.
3.a) Anytime the ECU (Motronic) is off-line because of any interlock conditions not being met (see list above in previous post), the engine-temp light will be OFF (and stay OFF) just after ignition is turned ON. ALSO, in same logic, fuel-pump will not prime.
3.b) Exception to above item: whenever the Reverser Knob is in Reverse position -OR- the Reverser-knob 4 contacts microswitch is defective, the Starter will refuse to engage BUT the RED engine-temp warning will still show ON (as if all the interlocks were all satisfied).
4) Of course, one must know if his engine-temp warning light was functioning before his ordeal (bulb not burned or removed). I would bet most K1200LT owner do not pay attention to this warning light after ignition is turned ON ... although many eventually pay attention to fuel-pump priming noise for troubleshooting puposes ;-)