Eureka! After replacing the starter relay purchased on eBay with the original Honda one the engine starts and runs perfectly!
UPDATE: installed a new fully charged battery = still no life to the starter motor.
PREVIOUSLY REPLACED: starter motor, starter relay switch, fuel cut-off relay
R1. the starter motor is directly connected to the battery(+), grounded (-), additional
R2. the 4P* starter switch works = starter relay switch clicks only (noticed a tiny connection spark)
R3. no dimming of lights in the process (no clutch switch, kill switch, stand switch active)
R4. 30A fuse in starter switch is good (connects to ignition switch (R), to regulator rectifier (R/W), and to starter relay switch)
(4P*: G/R to clutch switch and clutch diode, Y/R to starter switch, R/W to fuse and regulator rectifier, R to ignition switch)
Looking at the wiring diagram:
W1. the starter relay switch has wire G/R connecting to clutch switch (inactive) and to clutch diode (inactive)
W2. the starter relay switch has wire Y/R connecting to MINI 9P to starter switch (the kicker)
All these work fine (by deduction)
The starter motor receives no power, not turning/cranking to initiate the firing cycle in the chambers/spark plugs.
I therefor suspect a possible failure in the starter switch in its primary action.
I am excluding failures of other secondary parts/connections since the primary cycle seems not requiring them.
a. The continuity in the starter relay switch
b. Direct connection battery-starter motor (bypassing starter relay switch**)
** un/checked the voltage at the starter motor
All lights work at the turn of the ignition key.
The starter switch produces a single "click" in the starter relay (just replaced).
A new starter motor has been installed.
The battery shows 12.+ Vlt. and was tested as "good"
New spark plugs. Carbs are clean.
What can be the problem?
The well maintained/serviced motorcycle had zero problems up to this one. (1998 Honda Pacific Coast 800)