Symptoms: New stator - when cold, all SEEMS to be fine - when hot - output as indicated by bike's voltmeter seems to be reduced from 13.5 - right around 12 - at idle, w/brake on, Voltmeter indicates about 10 volt output.

All diagnostic tests (AC output, DC output measured across battery terminals, Diode test, Regulator ground, Stator ground) seem to have results within normal.

Has anyone ever experienced an intermittent failure on a voltage regulator?

Any way to test the main breaker to see if resistance through it is too high? (if contacts were cruddy, I could see heat-related resistance creating a problem).

I'd appreciate any thoughts - I like this old bike, and w/a new stator, I don't think I should be seein' what I am.

 

What is its output when you rev it? Usually when a regulator goes crook it will overcharge....if you see 16v when revving then its stuffed. Don't check voltage with anything other than its usual stuff working, so no brake on, just unloaded and it should read 12.75 and above and go up to about 14.25 when you rev it.

By doing it this way you know that faulty accessories etc are not affecting the readings.

 

Also I have noticed that my bike's volt gauge reads lower than actual battery voltage. I have heard the same thing from other people as well. Plus at idle, you're not going to get full output, usually not even half output. Mine also drops to around 10 at idle with the brakes on. Don't forget the brake light circuit and the anti-dive valve that operates off the brake light circuit.

 

I recently fixed a charging issue on my 83 FXR - bad regulator ( that killed my battery { because of shorted wire } ).
Measure at the output of the stator, Vac increases w/ rpm's? Yes. Measure across the terminals of the battery. Vdc increases? No. Wires good? Battery good? Bad regulator.
A new regulator costs less than an hour of t-shooting by my local HD dealer.
Spanners tells you, too much VDC reving is bad. Digger tells you that over draw of current is bad. These guys are what make this site great.

 

D1gger, none of the bike gauges are very accurate. You've done the right thing by comparing your voltmeter with a test meter. That way you know what the gauge is actually telling you!

 

As I said - Volt Meter in the bikes dash is showing just over 12.5/13 volts - it never goes above 13.

Measuring DC voltage at battery terminals when bike is running above 2K RPM shows about 13.8 volts

But - while on a long ride/hot day, the output as shown on the voltmeter seems to gradually diminish. It's this "trend" that I'm worried about - and want to understand. The bike's 28 years old, and these are the original gauges, so it's indeed possible that the voltmeter in the dash is just inaccurate. I suppose I will bring my digital voltmeter, and pull over and double check DC output when I start noticing the degradation.

Thanks for all the suggestions, folks - the input is appreciated!

 

Disregard the factory gauges, use a digital mutimeter to test at the battery. And whatever you do, do not lert anyone tell you to disconnect the battery while it is running. You have electronics in the charging system and when you disconnect the battery you have nowhere for the electrons to flow. There are only 2 things in your RT that charge the battery, the voltage regulator and the stator. A stator either works or it doesnt, simple as that, it creates alternating current to the voltage regulator. The voltage regulator has 3 diodes or a diode bridge that filters or converts the Alternating Current (AC) to Direct Current (DC). Your battery is DC so the vlotage regulator is monitoring the voltage of the battery and when voltage drops below the setpoint built into the regulator, it switches to charge mode and by converting AC to DC, charges the battery. You have intermittent issues which seem to be heat related and would suggest your voltage regulator is failing. You should also check the rubber plug at the front of the crankcase. Sometimes you can have a bad connection on the pins and connector which will not allow the AC to reach the regulator. You should also have a spring clip holding the rubber connector into the cranckcase. Make sure you have a clean, dry, oil free connection and the retainer clip.