Charging '101'
Yamaha Road Star
Charging problems can drive you up the wall.  Adding to this is the fact that
there seems to be no easy way for us simpleton's to verify that the Regulator/Recitifier
is good or faulty. This primer goes along that line, as does the Yamaha Service Manual.
The Service Manual leaves some to be desired and I hope I've explained it a bit
further so you can successfully troubleshoot your charging circuit.
The main idea is to verify that your stator is either good or bad and that your circuit
wiring is good or bad. If after running this troubleshooting procedure and no faults
are found, it leaves only one logical option, a bad Regulator/Rectifier.
The charge circuit is quite simple.  We first have to absolutely qualify or
disqualify the stator and associated wiring, we then can reasonably determine that
the R/R is either good or faulty.
1.   Start off with a fully charged battery.
      Set your multimeter on the 50V DC range and hook to battery,
      You should read 12.6VDC to 12.8VDC 
2.    With meter still attached, Start your engine and read voltage.
       You should be reading between 13.5VDC and 14VDC
       If this is true then your charge system is OK.
       If your charge rate is higher than 14VDC you have a possible bad regulator
       and your battery is in danger of being damaged from overcharging. 
       If voltage is lower than 13.5VDC then go to step # 3.
3.    Disconnect the 5 pin connector, 'A', at the top of the Regulator / Rectifier.
       Check for corrosion, if a problem is present, then clean all connections and
       re-try step #2.
       If no problem is seen then proceed to step #4.

Click on image for larger view
Remove vinyl cover and depress catch and
pull upward on connector.
B =  Black ground,  R = Red Battery Pos +
W = White wires from Stator windings
4.    Set your multimeter to the Ohm's scale X 1
       Open up the Left-hand side cover, in front of the battery,  a cable clamp with several
       bundles of wire and connectors are present, one connector has 3 white wires 
       going in and out of the opposing connector.
       This is connector 'B' in the diagram below.
       Hold one test lead to any stator lead.
       Hold other test lead to any other stator lead. Note reading. 
       Repeat at all pairs of test leads 
       Equal readings should be obtained at each pair of stator leads.
       Your readings should be between .45 ~ .55 ohms on all three pin sets of the plug.
       If readings are + or - a bit , do not automatically decide the stator is bad, temperature,
       materials, and tools can give a fluxuation of readings. We are looking for a reading close 
       and equal to the .45 ~.55 ohms specified. A reading of .6 is not unuseal.
       If not, then stator has open or has shorted windings or open wire from
       connector to stator windings, repair wire or replace stator.
       If readings are Ok then proceed to Step #5.

Click on image for larger view
5.    If all 3 readings are within specified range then insert meter probe into each pin of
       connector to the motorcycle frame (ground). 
       If any reading is less than infinity, then the stator is grounded. 
       Replace Stator.
       If readings are infinite then go to step #6
6.    If the stator checks good then,
       Set multimeter to 50VCD range and insert probes into the Red and Black wired pins
       on the R/R connector (connector A). 
               click to enlarge
       You should read battery voltage.  If not, Main Fuse is bad or an open wire is present.
      Replace Main Fuse or look for open wire.
       If battery voltage is present then Main Fuse and wiring are OK.
       Goto Step #7.
7.    Check wiring continuity between connector 'A' and connector 'B', with multimeter
       set on the ohm's scale at X 1.  The readings are taken from the "white" wires.

                   This the larger "B" connector with spade pins.
                                                    its wires run directly to the "A" connector. 

       If a reading of infinity is present in any wire then repair open wire. 
       If all wires show continuity then proceed to Step #8.

8.    If the stator has checked Ok, 
       battery voltage is present on Red and Black pins of (A),
       and all wiring is intact. 
       Goto Step #9
9.    Set multimeter to 200VAC scale, 
       Start your engine leave at idle
       Hold one test lead to any stator lead on connector 'B'. 
       Hold other test lead to any other stator lead. Note reading. 
       At idle you should read @ 30VAC
       Repeat on all pairs of leads. 
       Equal readings should be obtained at each pair of stator leads.
       Rev engine to @ 1500 RPM's and repeat voltage readings,
       Equal readings of @ 80VAC should be obtained at each pair of stator leads.

      If reading are all equal and in range then reconnect the (B) connector in front of battery
       and re-check the readings at the "W" terminals on the "A" connector. The readings
       should be the same as at the previous connector. If in range and equal on each pair.
       We have verified that your Stator windings and associated wiring are intact, 
       Regulator / Rectifier is bad, Replace

      If readings are not in range and equal for each pair of pins, then stator has open wire,
       shorted, open winding, connections are breaking down, or open wire, 
       retrace steps #3 thru #9 to verify problem.