Charging issues

[Phare Est]

I thought I had fixed a tach and charging problem on my '81 XS1100 Midnight Special over the summer by fiddling with the three white wires going from the stator to the REG/REC behind the fuse box. Finally, the charging system was working as it should. I figured it had been a simple wiring issue.

But recently, I changed the crankcase cover gasket, and all of a sudden, the charging system started acting up again... I checked the stator, the field coil and the REG/REC with a multimeter: the readings haven't changed from the last time they were checked a few months ago. Strange goings-on...

The same thing happens every time. The battery needs to be fully charged (at least 12.9 volts) for the tach needle to move, and for the tach light, the speedometer light and the headlight to turn on when I start the bike. The tach needle moves for about 10 seconds, then it goes down to the 0 rpm mark (where it stays). If I then turn off the ignition and fire the bike back up, none of the aforementioned lights turn on and the tach needle does not move.

Where could the problem lie? I'm a bit at a loss.

[motoman]

My bet is where that wire loom goes alongside crankcase pan has gotten pinched somewhere.....or clean that large plug-in behind the fuse panel as this is where loom runs to, and is a notorious location for voltage drop output from alt..

[Phare Est]

My bet is where that wire loom goes alongside crankcase pan has gotten pinched somewhere.....or clean that large plug-in behind the fuse panel as this is where loom runs to, and is a notorious location for voltage drop output from alt..

Thanks for the advice motoman. I cleaned the large plug-in behind the fuse box many times, so the problem lies elsewhere. I checked the REG/REC, the stator and the field coil one more time with the multimeter : all readings are good (according to the shop manual). And I'm quite sure there's no pinched wire going from the stator and the field coil to the plug-ins.

Could there be a burnt or otherwise damaged wire under the insulation somewhere? In that case, would the readings from the multimeter still be correct? Could the actual flywheel be the problem?

Thanks so much for your help! ☺

[motoman]

Thanks for the advice motoman. I cleaned the large plug-in behind the fuse box many times, so the problem lies elsewhere. I checked the REG/REC, the stator and the field coil one more time with the multimeter : all readings are good (according to the shop manual). And I'm quite sure there's no pinched wire going from the stator and the field coil to the plug-ins.

Could there be a burnt or otherwise damaged wire under the insulation somewhere? In that case, would the readings from the multimeter still be correct? Could the actual flywheel be the problem?

Thanks so much for your help! ☺

Most welcome! Where things are at now with your issue kinda goes beyond my own experience with what I have had to deal with. Having said that, not going to just make guesses. I suggest that 3Phase, or a member here that has had to test electrikery on these scoots through-out the whole system steer you in correct direction.

[TopCatGr58]

Hey there,

I'm not an electrical guru, but I can suggest a few things to check while waiting for Scott-3Phase/CaptonZap or others to reply.

First, take your multimeter on VOLTS, and get the bike running, put the meter on the battery terminals, and rev the bike to 2500 rpm. Should get ~14.5 Volts. IF only 12 or less, then the charging system isn't working.

IF not charging, next get a jumper wire and connect it to the Green wire of the 3 wire plug from the reg/rect to the field coil, leaving it plugged into the field coil, but ground the jumper to a good ground, and again measure the battery voltage at 2500 rpm. If NOW getting ~14.5 V, then field coil works, but Reg/rect is suspect. IF still 12V, use a single steel feeler gauge and see if it will stick to the ALT cover. If so..then field coil generating magnetic field. If it doesn't stick to alt, then field coil isn't generating magnetic field.

IF sticks and only 12V or less, again Reg/Rect is suspect, but also ALT may be suspect....but if you got good resistance meter readings on the ALT 3 white wires AND OPEN when checking from any white wire to ALT casing, then it's not shorting to ground, and that points more towards the Reg/Rect.

T.C.

[3Phase]

I See The Light

I thought I had fixed a tach and charging problem on my '81 XS1100 Midnight Special over the summer by fiddling with the three white wires going from the stator to the REG/REC behind the fuse box. Finally, the charging system was working as it should. I figured it had been a simple wiring issue.

But recently, I changed the crankcase cover gasket, and all of a sudden, the charging system started acting up again... I checked the stator, the field coil and the REG/REC with a multimeter: the readings haven't changed from the last time they were checked a few months ago. Strange goings-on...

The same thing happens every time. The battery needs to be fully charged (at least 12.9 volts) for the tach needle to move, and for the tach light, the speedometer light and the headlight to turn on when I start the bike. The tach needle moves for about 10 seconds, then it goes down to the 0 rpm mark (where it stays). If I then turn off the ignition and fire the bike back up, none of the aforementioned lights turn on and the tach needle does not move.

Where could the problem lie? I'm a bit at a loss.

Phare Est,

What crankcase cover gasket did you change? That should have nothing to do with the electrical system unless you pinched a wire.

If the bike starts and runs then the MAIN fuse is probably good along with the ignition switch and the ignition switch connector in the headlight shell.

As T.C. suggested, ground the Green wire for the 3-pole Regulator connector to full-field the alternator and check the battery voltage with the engine running over 2,000 RPM, it should be over 14 Volts. The charging system is almost identical to the old Chrysler charging system. The Brown wire is voltage sense and also supplies 12 Volts to the field coil. The Green wire is the ground return from the field coil and the Regulator varies the ground to regulate the voltage. Ground the Green wire -- full voltage and current from the alternator that will let the smoke out of the electrical system and wreck the battery if you run it too long so just test it, then stop doing that.

The tachometer runs straight off of one of the three White wires at the Regulator/Rectifier connector. If the tach's not working then the alternator isn't working, the tach connector in the headlight shell is dirty/burned or the tach is toast.


The instrument lights are supposed to come on with the headlight when the headlight relay closes after the engine starts and the alternator is working.

There is a diode inline on a second White wire at the Regulator/Rectifier connector that runs up to the headlight relay. If the lights aren't working then the 20 Amp HEAD fuse could be bad or just loose in the fuse block, the alternator isn't working, the diode could be bad or the headlight relay could be bad.

Unplug the headlight relay and put a jumper wire between the Red/White wire and the Blue wire to bypass the relay. The lights should come on when you turn on the ignition switch but they'll work off the battery so if the tach's not working then you won't have a clue if the alternator is working or not.

[Phare Est]

Phare Est,

What crankcase cover gasket did you change? That should have nothing to do with the electrical system unless you pinched a wire.

If the bike starts and runs then the MAIN fuse is probably good along with the ignition switch and the ignition switch connector in the headlight shell.

As T.C. suggested, ground the Green wire for the 3-pole Regulator connector to full-field the alternator and check the battery voltage with the engine running over 2,000 RPM, it should be over 14 Volts. The charging system is almost identical to the old Chrysler charging system. The Brown wire is voltage sense and also supplies 12 Volts to the field coil. The Green wire is the ground return from the field coil and the Regulator varies the ground to regulate the voltage. Ground the Green wire -- full voltage and current from the alternator that will let the smoke out of the electrical system and wreck the battery if you run it too long so just test it, then stop doing that.

The tachometer runs straight off of one of the three White wires at the Regulator/Rectifier connector. If the tach's not working then the alternator isn't working, the tach connector in the headlight shell is dirty/burned or the tach is toast.


The instrument lights are supposed to come on with the headlight when the headlight relay closes after the engine starts and the alternator is working.

There is a diode inline on a second White wire at the Regulator/Rectifier connector that runs up to the headlight relay. If the lights aren't working then the 20 Amp HEAD fuse could be bad or just loose in the fuse block, the alternator isn't working, the diode could be bad or the headlight relay could be bad.

Unplug the headlight relay and put a jumper wire between the Red/White wire and the Blue wire to bypass the relay. The lights should come on when you turn on the ignition switch but they'll work off the battery so if the tach's not working then you won't have a clue if the alternator is working or not.

Thank you TopCatGr58 and 3Phase for the wealth of information!

I changed the alternator cover gasket, and I'm quite sure no wires were pinched in the process.

I started by following TopCatGr58's advice and may have pinpointed the cause of my charging problem. I tested the charging system again with the bike running : the multimeter, when hooked to the battery terminals, always reads 12 volts, even when the engine is revved. I grounded the green wire going from the field coil to the REG/REC : the multimeter still read 12 volts when the engine was revved. I then put a thin feeler gauge against the alternator cover while the bike was running : the gauge did not stick to the cover... I revved the engine again, but absolutely nothing happened to the feeler gauge. It doesn't look like the field coil is generating any kind of magnetic field.

When I check the brown and green wires coming out of the field coil, the multimeter reads 3.5 ohms, then 3.6 ohms when I switch the multimeter probes. Why isn't the field coil generating a magnetic field? Could it be a flywheel issue?

[skids]

I revved the engine again, but absolutely nothing happened to the feeler gauge. It doesn't look like the field coil is generating any kind of magnetic field.

When I check the brown and green wires coming out of the field coil, the multimeter reads 3.5 ohms, then 3.6 ohms when I switch the multimeter probes. Why isn't the field coil generating a magnetic field? Could it be a flywheel issue?

There is nothing that can go wrong with the "flywheel" aka "rotor". It is just a metal object that spins and has holes to vary the magnetic field. The field coil should come on with the key whether or not the engine is running. I had a field coil burn-up once. I can't tell you that this is the case you you with the resistance/continuity check. You might want to check for voltage at the clip to the field coil. Dirty connection at the clip???

[skids]

Whatever you do, don't remove the screws that hold the stator to the case while it is installed on the bike. There is little clearance with the rotor with the stator and it will drop down causing damage to the windings.

[3Phase]

Whatever you do, don't remove the screws that hold the stator to the case while it is installed on the bike. There is little clearance with the rotor with the stator and it will drop down causing damage to the windings.

What skids said.

The headlight relay connector actually has a Red/Yellow wire, not Red/White. Sorry about that.

If the field coil continuity/resistance is good, check the voltage on the harness connector with the Regulator unplugged.

The Brown wire comes from a splice on the main Brown wire (switched power) from the ignition switch. There are no connectors after the switch until it reaches the fuse block so you should see battery voltage on the Brown and Green wires when you turn on the ignition switch.

If you've got battery voltage, I don't have a clue what's wrong unless the field coil is shorted to ground. Check the continuity between the Brown and Green wires to ground, they should both show infinity.

Edit: The resistance between any White wire to any other White wire at the Rectifier connector should be 0.4 Ohms.

[Phare Est]

If the field coil continuity/resistance is good, check the voltage on the harness connector with the Regulator unplugged.

The Brown wire comes from a splice on the main Brown wire (switched power) from the ignition switch. There are no connectors after the switch until it reaches the fuse block so you should see battery voltage on the Brown and Green wires when you turn on the ignition switch.

Hi 3Phase,

I checked the voltage on the harness connector with the REG/REC unglugged and the ignition switch turned on. The brown wire reads 12 volts on the multimeter, but there is almost nothing coming out of the green wire (0.2 volts). Is this normal?

[TopCatGr58]

Hey,

Pitching in for Scott, the Green wire is the GROUND that the Reg/Rect controls/modulates to control how much current/voltage is going INTO the field coil. So...the green wire shouldn't read any voltage.

What he said was to put the ohmmeter probes onto the brown wire connector/pin on the Field Coil connector, and the other probe on the engine/frame/ground point. Do the same thing with the brown wire. You are testing the wires TO the field coil, NOT the wires on the bike's HARNESS side. Unplug the field coil plug from the harness before testing. You should NOT get any continuity=infinity resistance. IF you find or are able to measure resistance with either the brown or green wire tested, then there's a SHORT in the wires of the field coil allowing current/voltage to go directly to GROUND and not power/energize the field coil. REPLACE the field coil.

T.C.

[skids]

Hey,

Pitching in for Scott, the Green wire is the GROUND that the Reg/Rect controls/modulates to control how much current/voltage is going INTO the field coil. So...the green wire shouldn't read any voltage.

What he said was to put the ohmmeter probes onto the brown wire connector/pin on the Field Coil connector, and the other probe on the engine/frame/ground point. Do the same thing with the brown wire. You are testing the wires TO the field coil, NOT the wires on the bike's HARNESS side. Unplug the field coil plug from the harness before testing. You should NOT get any continuity=infinity resistance. IF you find or are able to measure resistance with either the brown or green wire tested, then there's a SHORT in the wires of the field coil allowing current/voltage to go directly to GROUND and not power/energize the field coil. REPLACE the field coil.

T.C.

And this test is with the key in the off position of course.

[Phare Est]

Hey,

Pitching in for Scott, the Green wire is the GROUND that the Reg/Rect controls/modulates to control how much current/voltage is going INTO the field coil. So...the green wire shouldn't read any voltage.

What he said was to put the ohmmeter probes onto the brown wire connector/pin on the Field Coil connector, and the other probe on the engine/frame/ground point. Do the same thing with the brown wire. You are testing the wires TO the field coil, NOT the wires on the bike's HARNESS side. Unplug the field coil plug from the harness before testing. You should NOT get any continuity=infinity resistance. IF you find or are able to measure resistance with either the brown or green wire tested, then there's a SHORT in the wires of the field coil allowing current/voltage to go directly to GROUND and not power/energize the field coil. REPLACE the field coil.

T.C.

Hi Skids and TopCatGr58,

Thank you so much for your advice. I did the tests and there doesn't seem to be any resistance with the brown and green wires.

That being said, I will be replacing the three white wires going from the plug-in behind the fuse box to the REG/REC. When I disconnected the five prong plug-in at the REG/REC (harness side) and tried to measure the ohms coming from the alternator, I discovered something odd : the readings were out of whack compared to the ones I got at the plug-in behind the fuse box. This would be indicative of a wiring issue, would it not?

[skids]

Hi Skids and TopCatGr58,

Thank you so much for your advice. I did the tests and there doesn't seem to be any resistance with the brown and green wires.

That being said, I will be replacing the three white wires going from the plug-in behind the fuse box to the REG/REC. When I disconnected the five prong plug-in at the REG/REC (harness side) and tried to measure the ohms coming from the alternator, I discovered something odd : the readings were out of whack compared to the ones I got at the plug-in behind the fuse box. This would be indicative of a wiring issue, would it not?

Sorry, I am a bit "dense." I need a better description on what side of what clip you did your measurements and what connectors you touched with the probes. Also, when you say "out of whack", what were the readings? Keep in mind that corrosion in a wiring clip is usually the culprit, meaning ripping out wiring is not a solution for that.