Forget about resistance measurements with the RR. Again, there can be subtle changes with suppliers to Hyo and the manual specs may not be accurate.
What is important is the voltage readings at the RR and battery terminals whilst you are riding and the RR is charging.
The only way to truly test this is with a volt meter whilst you are riding.
For a stationary test you need to have your battery at full charge to start with, so hook up that battery charger at one tenth capacity for 12-14 hours.
On disconnection from the charger the battery should read 13.2V DC or higher. It will drop back down on standing.
Start the engine and when warm get the revs up to approx. half way (5000rpm) and read the battery terminal voltage.
The Hyo diode RR should be throwing out around 15 volts. Due to the severely under spec wiring used by Hyo, there is a considerable voltage drop when you draw down from the battery. If the voltage is down just a little bit you will get the dreaded red FI light. The bike will run as normal but the ECU has detected an out-of-spec reading and "bling" up comes the FI warning.
Replacing the RR with a MOSFET one may not eliminate that FI light. A MOSFET RR is going to be supremely efficient and chuck out a steady 14.2 volts but your wiring loom may still let you down.
I have had the same issue with my GV650C.
Dead diode based RRs on a couple of occasions. Finally bit the bullet and shelled out for an expensive MOSFET unit. Bike ran much better with a steady 13.9 volts at all rpm, but the FI light randomly came on with no other appearent symptoms.
I had been utilising the existing wiring loom and when I duplicated the wires direct to the battery, 'Voila', 14.2Volts at all rpm and no more drama.
I ordered the RR from http://www.roadstercycle.com
with the Triumph harness and utilised two of the four (duplicated) RR output wires on a series 250 2 pin socket plugged into the existing wiring loom, and the other 2 (initially heat shrunk) to another series 250 2 pin plug and socket direct to the battery terminals with a 30amp self resetting circuit breaker (snapped off the mounting plate and used a piece of large heat shrink tubing).https://picasaweb.google.com/109697641141633861827/Shindengen_RR_Upgrade?authkey=Gv1sRgCM37mqGco7mjPw#slideshow/6069909535354830210
$2.60 a meter (Check out their cut your own length spools)