Bike is a 1991 FLHTC with 77k miles.

I was about 10 miles from home and noticed my signals weren’t working. A quick look at the voltmeter showed only 10 volts. The voltmeter always has shown 2 volts less than what is measured at the battery - usually shows 12.5. I charged the battery overnight and started tracing down the problem. Battery is a year old.

First I checked the battery:
Voltage at battery with ignition off – 12.9
Voltage at battery with ignition on – 12.3
Voltage at battery with engine running (2k rpm) – 12.3...not good - usually see about 14.

I unplugged the voltage regulator and tested each of the stator contacts to ground. Stator isn’t shorted to ground. I also checked continuity between the stator contacts. Stator isn’t shorted to itself. I also checked the AC voltage with the engine running. Getting 40 volts at 2k rpm – perfect.

All of this points to the regulator being bad. I bought a new one, mounted it up, plugged it into the stator plug and ran the lead to the silver contact on the 30 amp breaker. Still no dice – voltmeter shows 10 volts and 12.3 volts at the battery while the engine is running.

Could there be a short or open circuit after the breaker? I appreciate any help.

 

test the voltage at the breaker both side should be the same if it is working if not replace it. or do a voltage drop across the breaker it should not drop more then 0.2 volts. max 0.5 volts. test for output voltage at the stator under load, back prob the regulator at 1500 rpm and you should have 35 volts or more. make sure the regulator is grounded or it will not work.

 

I did measure from the post on the breaker to a good ground and ot the same voltage as I did when I measured between posts on the battery (12.8), so the circuit after the breaker is probably in good shape. Did this while the bike was not running. Checked continuity as well from both posts and all looks good there.

I guess I should have measured what was coming from the regulator lead in the first place, right...lol? It's only 5 volts. So, i'm thinking that either I bought a faulty regulator or the stator is toast. I don't know how the stator is bad if it is putting out the proper voltage. It also passsed the other tests - not shorted to ground. Also, measured across the stator plug - getting .5 ohms. Anyway, I went back and made doubly sure that I'm getting a good ground at the regulator mount. Still only 5v from the regulator lead. I should be getting 13v +, right?

 

Dr. Hess's how to test your charging system

Scale on DC Volts, around 20V max voltage scale. Nominal readings are given in brackets. Check voltage across battery terminals (12.8). Turn bike on. Check voltage (less than previous, ~12.0+, depending on headlight, accessories). Start bike and let idle. Check voltage (could be 12.0 to 15). Rev to about 2500. Check voltage (should be more than observed with bike on but motor not running, and more than with bike off. Ideally between 13 and 15.) Turn high beam on. Should be about the same, give or take a little. If the voltage is over 15 or 15.5-ish with a headlight on, I'd consider replacing the regulator and/or checking all grounds (battery to frame, regulator to frame in particular). If the battery voltage with the headlight on, bike not running is less than around 11.5-ish, I’d replace the battery. If it’s 10, it’s past it’s prime.

If you pass the above tests, your system is most likely fine, including the regulator and stator. If you don't pass, then:

Bike off. Meter set on Ohms, medium-ish scale, like 20K or 200K Ohms max scale, depending on your meter. Pull stator plug. Ground the meter black lead to a good chassis ground, like a bolt or even the battery negative. With the red lead, touch a different part of the bike, like the engine case at an unpainted part or another bolt. Meter should read low ohms, like 0. If it doesn’t, you didn’t ground the black lead. With the red lead, touch each contact on the motor side (stator) of the plug (the part stuck in the case). Depending on if your case has a male or female plug, if you can't see the metal part/pin of the plug, you can put a paper clip in the hole and touch the paperclip with your meter red. Meter reading should be infinity on all pins. If it isn't, your stator is shorted to the case, replace.

The following is for single phase systems. I don't have a multi-phase and haven't had to diagnose anyone elses, so I haven't dug into those systems.

Set meter to lowest ohm scale, like 200 Ohms, typically. (Note: Not 200K ohms). Check resistance between the two stator plug pins. Should be fairly low. My Book says 0.2-0.4 ohms. The spec is in your shop manual. If it is infinity, stator is blown open. If it is 0, stator is shorted to itself.


Set meter to AC Volts, 100V scale. Attach each meter lead to a stator pin. You may need to rig up some type of temporary plug. It is important that nothing can short to ground or to each other accidentally, or you will blow the stator if it wasn't blown before. An old plug off of your last regulator is a good way to do it, but, get creative and be careful. I can do it holidng the leads on the pins once the bike is running, but I don't like to. Start bike. Voltage should vary with engine speed. Specs are in your shop manual, but 35V at a couple thousand RPM is probably about right. My book says 19-26 V / 1K RPM.

If you passed that stator test and failed the first test, your regulator is shot. If you failed any part of the stator test, replace both regulator and stator.

 

Thanks THC.

I was doing some searching last week and actually printed Dr. Hess's cheatsheet off. It is what I had been basing my tests on.

I'm going to run thru them again tonite. I'll post my findings.

Thanks again.

 

Here is a slightly different one if it helps.

Testing Harley Davidson Charging Systems

Important information about Harley Davidson full wave charging systems (covering 70-05 Touring, 84-07 XL, 84-00 Softail, 91-03 Dynas, All FXR’s)
1. Battery Test:
The battery needs to be a fully charged battery that has been load tested to ensure proper readings. If you are not working with a fully charged and functional battery, all other voltage tests will be incorrect. Most places like Auto Zone, Advance Auto, and Pep Boys will charge and test motorcycle batteries for free. Standing battery Voltage should be 12.5-13.2 DCV.
2. Charging System Voltage Test:
Start motorcycle, Measure DC Volts across the battery terminals (you should have a reading of approximately 13.2-15 DC Volts).
3. Check Connections/Wires:
Inspect the regulator/stator plug, and check the battery terminals for connection/corrosion. If everything seems to be in order, move on to number 4 below to determine if there’s a failed component.
4. Stator Checks/Rotor Check:
Each of the following tests isolate the stator & Rotor, If AC Output test Fails and Resistance Check, and Stator IB Test Pass then Rotor is at fault (Pull Primary covers and inspect rotor for damage).


AC Output Check:
1. Unplug the regulator plug from the stator
2. Start motorcycle and change Voltmeter to AC volts.
3. Probe both stator wires with your meter leads.
4. The motorcycle should be putting out approximately 18-20 ACV per 1,000 rpm. (Reading will vary depending on system, check service manual specification)
5. Generic Specs:
· 22 amp system produces about 19-26 VAC per 1,000 rpm
· 32 amp system produces about 16-20 VAC per 1,000 rpm
· 45 amp system produces about 19-26 VAC per 1,000 rpm
Stator Resistance Check:
1. Switch your multi meter to Ohm x 1 scale.
2. Probe each stator wires with meter leads and check resistance on meter.
3. Resistance should be in the range of 0.1-0.5 Ohms. (Reading will vary depending on system, check service manual for specification)
4. Generic Specs:
· 22 amp system produces about 0.2 to 0.4 ohms
· 32 amp system produces about 0.1 to 0.2 ohms
· 45 amp system produces about 0.1 to 0.2 ohms
Stator IB test or Ground Check:
1. Switch your multi meter to Ohm x 1 scale.
2. Probe each stator wire with your positive lead on multi meter and the negative to ground.
3. There should be no continuity to ground on either wire.
4. If there is continuity to ground your stator is shorted to ground.
5. Regulator Test:
Each of the following tests isolates the regulator only, so if any of these tests fail, the regulator is at fault.
Identifying Wires:

• Battery Charge Lead- Wire going from regulator to battery positive.
• AC output leads- Wires coming from the Stator to regulator.
• Ground- Wire from Regulator to ground or regulator may be grounded via the physical bolting to chassis.

- Regulator Ground Test: Insure the regulator body is grounded or grounding wire is fastened tight to a good ground (you should verify this by checking continuity from regulator body to chassis ground).
- Fwd/Reverse Bias Test/Diode Test: This check is testing the Diode function to ensure it is regulating the AC current for the stator into DC Current.

• Switch multi meter to Diode Scale.
• Place your Multi meter positive lead on each AC output wire.
• Place your multi meter negative lead on the battery Charge wire.
• The meter should read voltage typically around .5 volts.
• Next, switch your multi meter leads putting the negative lead on the AC output wires and the Positive lead on the Battery Charge Wire.
• The reading should be Infinite.
• With your meter on the same setting, place your multi meter positive lead on the regulator ground wire or to the regulator directly, and then place your meter negative lead on the AC output leads.
• The meter should read voltage typically around .5 volts.
• Next, switch your multi meter leads putting the negative lead on the regulator ground and the Positive lead on the AC output wires.
• The reading should be Infinite.

 

Sounds like you followed my destructions well. I'm going with a bad new regulator. Do check the voltage at the end of the regulator output wire with the wire not connected to anything else and the motor running. If you have zero or <~13.8, that new regulator is toast. Also make sure your regulator is well grounded. Put your ohm meter on low resistance and check the regulator case with the red and the battery negative with the black. Should be very low.

 

Dr.Hess,

My manual says .1 - .2 as the resistance range between the two stator plug pins. My measurement is .4..... could this be an issue with my stator afterall?

 

No, I doubt it. It takes a pretty expensive DVM to measure resistance that low anyway. You have like zip output. That's a major fault and pretty easy to find. You are just overlooking it. Check the stator again, check the regulator output line by itself, hook it to the breaker, check again, etc.

 

I will go out on a limb here and suggest that your charging system is probably ok if you can ride the bike for 10 miles without it running the battery down etc.
If all other lights such as headlamp etc. are bright and normal ., your charging and bat. are ok.
Had same " no signal lamp operation " on my 90 FLT Police.
Check multi. plug connector at the signal light control box for worn or corroded terminals. On mine the box is located on the left fork tube inside the fairing looking from the front of the bike with one only multi.plug connector.