I just started having charging issues with my 87 a couple weeks ago.

I finally got around to checking a few things today. Fuses are all good. Bike starts and runs just fine.

I checked the 3 yellow wires from the stator.  I have 35 volts at idle and easily up to around 100 with the engine revved.

The large green connector under the seat and the 3 conductor white connector under the seat and on the rear fender just out from under the pillion seat get warm with the engine running.  Neither got hot just nice and warm.  I pulled them apart. One had a little corrosion so I hit them both with contact cleaner and then put some dielectric grease and put back together.  They still get warm.  The wires are also warm. Nothing showing any signs of melting or anything like that.  

Battery is 2 years old but charges up easily and holds charge for a couple week when it will start the bike, no problem. Connectors are tight and nice and clean.

I did not pull the pillion seat and look at the reg/rec.

Anyone have any ideas where to go next?

Thanks guys  

You can get the battery tested or just toss one in it.. Nothing quite screws a day up like getting somewhere and it won't start.
Resistors in electronic devices get warm. Resistive connectors do too. Before I started spending money I'd probably want to know what the condition of the battery really is. If it's shady,ditch it,man. If you do put one in I'd think making sure that those warm connections aren't warm due to being resistive. How long does it need to run to get them warm? How do the wires feel close to them?

Here's a little more info.

Battery load tested good.

Connectors cleaned well and reconnected.  No more heating issues.
Still have 37 volts on all 3 phases idling.  Around 100v when revved.

At the regulator output, I have 13.4v idling and around 14 when revved.  Kind of hard to get an exact reading...the meter wants to keep falling. I saw 13.9 and 14.something.  Sounds like it works to this point.

No matter how much I rev it, I never get any upward movement at the battery.  It just slowly goes down.

Looking at the wiring diagram, it appears that this lead goes to the always hot at the ignition switch, through the fuse (which has been tested good) and to the battery. I have battery power at the output of the regulator when the motorcycle is off. According to the wiring diagram, I should, I believe. This should indicate that the wiring is good.  I have checked the ground down by the clutch lever.  It is fine.  I have no resistance measured from the block to the battery connector.  Starts fine. I doesn't act like there a bad ground or anything. Cranks right over and starts.

EDIT:  I checked the regulator/rectifies per instructions here
      http://racetechelectric.com/ft-751-voltage-regulators.html
Everything tested fine.

Anybody have any suggestions where to look next?

Thanks
Steve

I checked it a while ago.  Got good continuity from the block to the battery connector.  I will check it again just to make sure.