kz900 not charging

1976 kz900
*50+vac across each pair of stator leads
*15+vdc exiting reg/rec 
*new battery (2 months old)

when the reg/rect is connected to the battery the voltage at the battery only reads 12.8v even though the reg/rect puts out 15+v when not connected to the battery. coils both read 3.8ohms. ive run it without the ignition switch in the system by jumping the wires(thinking maybe there was an issue in the switch drawing power)

anyone have ideas? 
thanks

Nothing wrong with that.
Static voltage of fully charged 12v battery should read around 12.6 to 12.8 volts.
The reg rec should limit the running charge voltage to around 13.8 to 14.4 volts and much more than that will eventually fry the batt.

 

the 12.8v is at 4k rpm is what i meant to say. Thats normal? I was expecting to see 13.5+ without lights or acc on. 
Thank you

get your voltmeter
put meter on DC V
Bike must be running
Do not disconnect any connectors when taking these measurements.

Put one probe on the battery positive and the other probe at the rectifier on the wire that is going to the positive battery terminal.
(note: your regulator rectifier are actually two separate units. You will probe the white wire coming out of the rectifier and the battery positive post)

Voltage should be as close to 0.0V as possible. If the voltage is higher than 0.5V, then you have too much resistance on that wire.
The reading must be steady as well.
If any of the readings fluctuate, then you have ghost voltage..this means you have a break in the wire.

You had 15+ volts but you had no load on that line..You need a load to measure the voltage drop.

Take your probe from the white wire and check the brown wire on the regulator connector.
voltage should be 0.0V as well.

move one probe to the negative battery post and place the other probe on the black/yellow wire at the regulator connector.
should be 0.0V

move the probe from the regulator black/yellow to the rectifier black/yellow.
0.0v here also



turn off bike




 

ive got an aftermarket rect/reg.

the running voltage between the RR positive to battery wire and the positive battery terminal was .015 at idle and .038 at 4k rpm 

Which wires do you have hooked up on that reg/rec?
Did you buy the reg/rec from a reputable source? (there are a lot of counterfeits out there)

Your positive cable connection to the reg/rec looks good.

Is there a fuse on the positive wire from the reg/rec to the battery?

Try the negative connection(measure dc v between the negative battery post and the negative wire on the reg/rec with the bike running)
should be 0.0v

Nessism may chime in as he knows more about this reg/rec than me.

That R/R looks to be a real deal Shindengen SH775.  None better.

You should see about 14.5 VDC across the battery at 5000 rpm.  Make sure the battery is fully charged while testing.

If less than, say, 14 VDC, you can try an experiment, where you run the negative and positive out from the R/R straight to the battery.  If the charging is still low, you have a bad stator, or possibly, the stator wiring to the R/R is bad.