|Frequently Asked Questions
Before you can suspect any charging system component of failing you first should check all the easy stuff. First make sure
all the cells in the battery have electrolyte up to the full line. Use a hydrometer (a fancy name for a tube with floating balls
in it) and check all the cells after the battery has been charged. You can get a hydrometer for only a few dollars at most
bike shops. The ones made for cars are way to big to use on 99% of bike batteries. Once you are sure you have a good
Next check all the connectors. The battery cables and all the other wiring connections should all be clean and tight. A weak
or dirty connection can cause poor charging system output. A melted plug is also a sign of a loose or dirty connector. The
heat comes from the resistance of completing the circuit through oxide (or oil and dirt) on the surface of the terminals. If
you use spray cleaner to flush out any plugs check for signs that the plug is being damaged from the solvent and discontinue
using it if there is. Also use an air nozzle (or caned air) to blow out the connectors after cleaning them. Some of the spray
lubes like WD-40 are good for cleaning out connectors but I do not endorse them as lubricants. Again check to make sure
the spray lube is not damaging the plastic plugs or insulators.
Bikes with mechanical voltage regulators may also need to have the points in the regulator cleaned or better yet replace it
with an all electronic voltage regulator.
If you still have a charging system problem after this, then start working your way through the charging system with an
electrical meter as described in the repair manual for your bike. If something doesn’t make sense, ask me and I’ll try to
make it clearer for you.
2. Do I need an expensive test meter to figure out what's wrong with my bike?
An inexpensive electrical multi-tester can be purchased for around $10~$20 at most home center stores. These are more
than adequate for diagnosing charging system problems and well worth the price. I wouldn't be with out an electrical meter
and I always have 2 or 3 of them around and I keep a small one in my bags when I travel.
For testing rectifiers, a small battery and a light bulb wired together will give you an adequate test light. So long as the light
goes on when you touch the ends of the leads together, it'll work for testing connections and rectifiers. This is a schematic
for a simple test light made with 2 AA batteries and a 3 volt flashlight bulb.
3. How do I to test a rectifier?
Start with one lead of the meter (or test light) to the positive lead on the rectifier. Touch the other test lead one at
a time to each of the AC terminals of the rectifier. At this point you will either have continuity or not but it should
be the same with all the AC terminals on the rectifier.
Swap the test leads (still working with the positive terminal of the rectifier) and repeat the test. This test should
have the opposite result as the previous test. Again the result should be the same for each of the AC leads.
Move on to the negative lead off the rectifier and repeat the 2 previous tests. This is test is easier with a test light
than with an electrical meter. The point is to check that power flows one way but not the other and the exact
numbers isn’t as important. If your meter has a buzzer for continuity, this works very well too. If the rectifier fails
all tests with a digital meter, it may not be the rectifier but that you're using the meter on the wrong scale. Set the
meter to the diode test function and test it again. If your meter doesn't have this, it's time for a new meter.
This will catch a bad rectifier 95% of the time. The rest of the time they only fail under load and will usually get
7. Diagnostics for 1979~1984 Honda 750~1100 DOHC fours (and SOHC CB650)
The following information also applies to the CB550 Nighthawk but the resistance on the field coil (black to white
wires) is lower. Honda has released an updated stator/field coil assembly for this bike (this is the only bike I know
that uses this arrangement) and I recommend calling the Honda dealer for this information as the manual may be
The first test is to test the voltage between the red wire on the rectifier / voltage regulator unit (do not unplug it for
this test) and ground with the bike running. If you're only getting battery voltage then you have a problem. If
you're getting over 15 volts then the regulator is bad.
At first all those wires look rather intimidating but once you break it down it's rather simple. Unplug both of the
connectors and use the test procedure above to test the rectifier part of the unit. The red wire is positive and the
green wire is negative and test them against the 3 yellow AC leads.
The next test is to test the voltage regulator. Plug the small plug from the regulator / rectifier back into the wiring
harness. With the ignition on but the bike not running and if the regulator is good, you should get less than battery
voltage between the black and white wires in the large plug from the regulator / rectifier. You can do this test with
the bike running but I find it usually doesn't make any difference.
If these test have positive results the next thing to check is the resistance on the rotor. Remove the alternator
cover and check the resistance between copper rings on the rotor. There should be 4.5 ~6 ohms resistance if it's
good. Most of the time when rotors are bad there will be either infinite resistance (completely burnt out) or less
than 2 ohms resistance (internally shorted.) Either way you're looking at getting a new rotor. If the rotor checks out
good the next step is to check the resistance between the black and white wires (with the alternator cover installed.)
Wiggle and tug slightly on these wires during this test. If the resistance changes at all during this test or is different
than the resistance between the copper rings on the rotor, the wires leading to the brushes (black and white wires)
will need to be replaced. The wires to the brushes going bad is more common than one ouw think
The next thing to check is stator. I left this test for last because this is the least likely thing to go wrong. There
should be about .5 to 1 ohm resistance between the yellow wires from the stator and infinite to ground if the unit is
6. All of the components in the charging system on my bike test out OK but it still doesn’t charge.
This is almost always caused by dirty, corroded or weak terminal connections. Corrosion on the terminals acts as a resister
dropping current flow and creating heat. The heat often ends up melting the plugs making the problem even worse. The
only fix is to clean all the connections and coat the terminals with dielectric grease to prevent them from corroding again.
For more info on how to take care of this problem, go to the connection cleaning and repair section.
9. If I plug a terminal into the wrong place in the housing, can I get it out?
This is easier than it looks but to avoid repeating myself, the description on how to do this is in connection cleaning
and repair section.
8. My bike drains the battery when sitting, how do I find out what's causing this?
Solder 2 wires on a turn signal bulb and insulate it generously with electrical tape. Disconnect the positive cable off the
battery and connect the turnsignal bulb in-line between the negative post on the battery and the battery cable (do not try and
run the bike with the bulb in the circuit.) With the ignition switch in the off position, the bulb should be out. If it's lit, then
something on your bike is draining power. To find this, start unplugging connectors until the light goes out. The thing you
unplug that makes the light go out is the problem.
It’s also possible that the main wiring harness has shorted wires but if that’s the case, your bike will be regularly blowing
4. Charging system diagnostics for older Honda singles and twins (Pre-1978)
First off, read the above articles. These things all need to be dealt with when you have a charging system problem.
There are 3 wires from the stator and depending on the year of your bike they will be different colors. From 1969 on the
colors were pink, yellow and white. The pink wire connects to a full charging coil, the yellow to a 2/3rds coil and the white
wire to a 1/3rd coil. The yellow and white wires connect in the headlight switch when the lights are turned on. What this
means to you is that the resistance from pink to white will be a little less than pink to yellow. You should get around 3/4 to
1 ohm from yellow to pink and somewhat less from pink to white. None of these 3 wires should have continuity to ground.
Check the stator with an ohm meter and if it passes these test then move on to checking the connections.
The white and yellow wires from the split coils are connected together (in the headlight switch) when the headlight is turned
on directing more power into the charging system. If the switch fails the charging system will not give full output. To
make this more confusing, most pre-1969 Hondas use the same system but with different wire colors from year to year and
sometimes model to model. On these bikes the brown wire usually represents the full charging coil and yellow and pink
wires are from the split charging coil. The best way to be sure is to check the wiring diagram in a repair manual for your
bike. The best fix is a new switch but they are usually no longer available. Some people bypass this and connect the white
and yellow wires together at the rectifier giving full charging all the time. This is only a good idea if you ride with the
headlight on all the time.
Proceed to the next article if you are still having problems.
10. Is there a cheaper alternative to the OEM sealed beam headlights?
If your bike has a 12 volt electrical system and headlight is larger than 5 ¼”, you can replace the bulb with an auto
sealed beam. This fix is perfect for many older bikes with 6" round headlights.
Take an old dead sealed beam and tape up the glass with duct tape, put it in a paper bag, then whack it with a
hammer in about the center of the lens. Carefully remove all the broken glass and discard it. With a die grinder or
similar tool cut out around the bulb so there is about a 1" hole in the back of the reflector. Purchase a car 5 1/4"
Halogen sealed beam and glue it in with a generous amount of silicone rubber sealant. You will need to get a plug
for the back of the car headlight but many larger Japanese bikes use the same plug and it should be easy to get one
at most motorcycle salvage shops.
This type auto headlight has an internal halogen bulb surrounded by a glass reflector and lens so if it gets hit by a
rock and gets a small hole in it, it'll keep on shining. This should run you about $7 for the sealed beam and you'll
use about a dollar's worth of sealer. It'll also be about 50% brighter but the Halogen bulb will draw a little more
For bikes with 7" round or odd shaped sealed beam headlights
Most 7" round sealed beams are directly replaceable with H4 lens/reflector assemblies that take a replaceable
bulb. However some OEM sealed beams have and odd mounting system and will need to be either spliced like
below or use a 7" glass sealed beam like above.
To make a spliced lens/reflector assembly carefully cut the factory sealed beam steel reflector about 1" above the
bulb with a die grinder with a cut off wheel. This will leave about a 2" diameter hole in the back of the unit. Take a
Automotive H4 headlight and cut it's lens about half way between the bulb and the lens. You will see that the back
of the H4 unit and the front of the stock sealed beam will be 2 cones that pretty much fit together. Clean them both
well and glue them together with high temp silicone sealer. It is very important to remember is to maintain the stock
bulb position in the sealed beam so that the lens doesn't over heat and crack and to get the correct light pattern.
You can cut to slits in the H4 reflector (from about 1/2" from the bulb to the edge of the cone so you can roll the
cone a little tighter. Be sure and give the high temp silicone sealer at least 24 hours to dry but over a weekend
would be better.
Do either of these modifications at your own risk. These instructions assume that you have some proficiency with
hand tools and always wear safety goggles and gloves when using a die grinder or breaking glass.
11. Do special orders cost more?
For the most part they're the same price and only take longer. If I have to use a lot more wire or get some special connectors I
do not normally have, then there will be a small additional charge.
12. Why don't the parts you sell look like the ones that came on my bike?
The parts I sell are of my own design and construction. Currently I cannot make parts that look like the ones from the OEM
supplier in Japan so I settle for ones that work better. If you don't like how my parts look, then perhaps they're not for you...
13. What if I'm in a bad mood and take it out on you?
Hit the road Jack, WE RETAIN THE RIGHT TO REFUSE SERVICE TO ANYONE.
14. What are the limitations on the guarantee?
There are no special terms to the guarantee on my parts but I expect them to be installed correctly as per my
instructions. Failed parts will be repaired or replaced at my discretion. Before retuning any parts you need to
eMail me and let me know you are having a problem. I’ll help you check it out so we know for certain that it’s the
part and not something else.
I do not pay return shipping but I pay the shipping of the replacement / repaired part to you (in USA and half of
shipping on replacements outside of the USA.) The guarantee is not transferable from bike to bike or from person
to person. How will I know if the part has been used on more than one bike? I won’t, so I trust you to be as honest
with me as I am with you.
16. Do I have to use on line payments to buy from you?
I accept money orders and cashiers checks by mail. Click on the link below for a mail order form.
17. Do you have other bike parts?
For the most part "what you see is what you get." I'm always looking for new stuff to add to my line but business growth is
moving rather slowly.
15. What is your return policy?
Returns for warranty or exchange only. No refunds, no exceptions. If you bought the wrong part, I'll work with you to
get it straightened out.
5. Why don’t you make a regulator for the old Honda singles and twins?
Change that, I now have a voltage regulator / rectifier unit that works great on the these old bikes. This unit is
built by an outside supplier to my specs but it's a great part that I'm happy to put my name on... See the
VRRPM2-HCB on the regulator/rectifier units page.
There are a few things to consider before buying one. First are you running any electrical accessories that
cannot handle a voltage spike over 14.5 volts? If all you are running is the stock lighting, this unit is only an
optional item, but if you've added a radio, electronic ignition or a GPS, a unit like my VRRPM2 is a necessary
addition to your bike.
18. Charging system diagnostics for 1969 ~1978 Honda SOHC Fours.
An analog meter is preferred but digital meter is OK for these tests but you'll have to take into consideration the
static resistance in the meter. This article assumes that you have basic proficiency with an electrical multi-meter.
Start by removing the left side cover and unplug the 8 or (9 pin on some models) plug from the alternator windings
to the wiring harness. Set the meter to the lowest resistance setting, Rx1 on an analog meter or 0 to 200 ohm scale
(sometimes only labeled 200) on a digital meter. On the engine side test the resistance between the yellow wires in
all combinations. You should get .5 to 1.2 ohms resistance here. Next check from the yellow wire to ground and you
should get infinite resistance (or the same resistance as air.)
Next check the resistance from the white to the green wire. The spec here is 4 to 6 ohms but I've found that a little
out either way is OK but more than 1 ohm out is usually bad. Next test either the white or green wire to ground and
you should get infinite resistance. The green wire plugs into a ground connection but when it's not connected to the
harness it shouldn't be grounded when unplugged.
If all this checks out, move to the wiring harness side of the plug and Test the green wire to ground. You should get
no detectable resistance here or in other words: the same resistance as when touching the meter probes together. If
this is all good, plug the 8 (or 9 pin on some bikes) plug back together.
Now set the meter to DC volts and unplug the voltage regulator. Turn on the main ignition switch but set the
handlebar switch to off. Check the voltage from positive to negative across the battery then check the voltage from
the black wire that would have plugged in to the voltage regulator to ground. If there is less at the black wire than
at the battery, you have a wiring problem. This can be tested by making up a fused jumper wire to run from the
positive side of the battery to the black wire on the regulator. Then run the bike and check the voltage output.
Assuming the power to the regulator OK: plug everything back together; turn on the main switch and the handlebar
switch off. Either hand a paper clip from string or use a .002 feeler gage blade and lay it up against the end of the
alternator case (where the screws are that hold the field coil are) then pull it away. The magnetism of field coil
should bend the gage or hold the paper clip when you try pull it away. This test proves that at least the regulator is
working a little.
Now test the rectifier as per article #3 on my FAQ page.
Set the meter back to the lowest resistance setting and test the resistance from the white wire to ground. You
should get the same reading here as before when you did the test from white to green at the plug. Any discrepancy
here is a wiring problem. Unplug the rectifier and check the resistance between the yellow wire and once again you
should get the same resistance as at the alternator plug.
If this is all OK then remove the ground wire from the battery then test the resistance between the red wire where
the rectifier plugs into the positive battery cable. Then test from the red wire to the rectifier to the red wire at the
ignition switch. There should be no detectable losses here.
Since the ignition switch is unplugged, test the resistance from red to black wires in the on position. Any detectable
resistance here is bad.
If you resolve all this and you bike still doesn't charge correctly, there is one more thing to do to prove the problem
is in the voltage regulator. Start by running the bike until it is warmed up enough to idle properly. Use a fused
jumper wire and jump power from the positive side of the batter directly to the white wire that plugs into the
regulator. This will give the bike full charging all the time so do not run the engine over 1500 RPM or you risk
boiling the battery and blowing bulbs. With the engine running test the voltage output at the rectifier to ground with
the engine running at idle and 1200 RPM. If you get good charging, you need a new voltage regulator.
19. Are the shipment insured? No, unless you choose express shipping on check out. We ship by
USPS priority mail. These shipments are trackable in the USA so insurance is not needed.
However Priority mail shipments are not trackable overseas and the cost of insurance is the same
as express so for these orders, we recommend all overseas shipments to be by express mail. We
are not liable for lost over seas shipments unless they are sent by express...
Note: many articles have been revised and a few that no longer apply have
been deleted. Many of the article number have changed.
20. Can your products be used with Anti gravity or lithium batteries
I do not support the use of AG or lithium batteries with our products. While some have had good luck
with using our products with them, we believe these new tech batteries are too finicky to guaranty things
will work properly... We would rather you use a regulator from someone else than be upset with us
when your AG battery splits open or lithium battery catches fire...
21. Why don't you have your phone number on your website?
I tend to keep odd hours and I'm often asleep when people want to call. Also I can talk about
bike stuff all day and when I do, I don't get any work done. Feel homered if I share my phone
number with you and please do not share it with others. It works much better for me to asswer
questions by eMail...