PO Box 98393
Atlanta, GA 30359-8393

Home - Catalog - How-To's - XJBikes.com Forum

The Ultimate Relay, Switch, Sensor, and Diodes Guide

Charging System Electrical Specifications:

Typically, most charging system problems are confined to the battery itself, or the alternator brushes. The other components.....the alternator rotor, the alternator stator, and the regulator-rectifier unit......are hardy little beasts, and unless damaged by voltage surges, short circuits, or other assaults, are usually not the cause of charging system problems.

Remember: when checking electrical components for their resistance values, it's not just the resistance of the component itself, but also of any sub-harness wiring leads which may factor into the resistance readings! The component itself may be electrically "good", but if the wires or, more likely, the wire end metal terminals are corroded, looses, etc..........then the problem with the wire or the terminal also becomes a problem for the component, too.......

Charging System Overview:

The following guide to understanding your charging system was contributed by Dwayne Verhey, extreme XJ-Wizard.

There are two main types of alternator systems commonly used on motorcycles. Both types depend on a magnetic field, created by magnets in the alternator rotor, to induce an electrical voltage and current flow in a stationary coil of wires-----the alternator stator. If you ever get confused as to which is which, just remember that the rotating component is the "rotating rotor", and the spaghetti-like bundle of wires is the fixed-in-place, "stationary stator"......

The first type is the permanent-magnet rotor system (used on Virago, V-max, and FJR models, among others). In these systems, the fixed-strength magnets in the spinning rotor generate a constant-strength magnetic field, and thus excite the stator coil constantly; thus the alternator puts out 100% current at all times and the voltage regulator merely serves to shunt any excess generated current to ground. The advantage of the permanent-magnet system is a reduced amount of system complexity, but at the cost of increased heat and power losses (since the alternator system is generating power, and thus using up engine horsepower, constantly).

The XJ-series of bikes follows the more common automotive model, which employs variable-strength electro-magnets in the rotor. In these systems, the variable-strength magnets in the spinning rotor, when energized, are used to form the magnetic field which excite the stator. The voltage regulator controls the voltage output by varying the input voltage applied to the rotor's electro-magnets, and thus varies the strength of the magnetic field. If the system voltage drops, the voltage regulator increases the voltage fed into the rotor electro-magnets, thus increasing the strength of the magnetic field that the magnets produce, and therefore increasing the excitation (output) from the stator....and thus the alternator output voltage increases.

In both systems, the stator windings are 3-phase. Each stator wiring bundle (there are 3 of them, and each bundle is called a "leg") kicks out similar voltage, but 120-degrees out of phase with the adjacent leg(s). The resulting AC currents are then rectified (changed) to DC current via a 3-phase bridge rectifier, made up of 6 diodes, such that current in any leg flowing in either direction is directed back into the system as 12-volts DC (actually, around 13.5 to 14.5 volts DC, when everything is working properly).

If you lose a leg, or even a single diode, it is possible to still achieve voltage if the load is minimal, but as current requirements increase, the alternator will not be able to meet the challenge and the battery will have to take up the slack. Of course, as the battery drains, the available voltage is reduced, so the maximum rotor field voltage is reduced, so the current output is reduced, so the battery has to take up more slack, so ....

If you suspect alternator issues, do the following checks, in this order:

- first check the resistance on the wires to the rotor. If resistances are out of spec, then check for dirty rotor commutator rings, corroded connections, etc.----all of these problems will reduce the available rotor field voltage.

- next, check the condition of the connectors from the stator to the rectifier (the 3 white wires). There's usually 2 connectors -- one from the alternator, often hidden behind the battery box, and the other near the regulator. Corrosion in these spots will reduce the stator's outputted current (bad corrosion will often melt the connector, as the outputted current turns into heat rather than being delivered to the battery).

- next, with the engine running, back-probe each of those 3 white wires at their connector to ensure voltage is being generated on each leg. NOTE: the voltage on those 3 white wires is AC, not DC, so be sure to set your voltmeter properly. AND, YOUR CHECK WILL BE BETWEEN WIRE PAIRS (wire #1 to #2, wire #2 to #3, and wire #1 to #3….and it doesn’t matter which one you consider wire #1 or #2 or #3 to be, as long as each wire’s output is checked)……AND NOT TO THE FRAME OR (GOD HELP YOU) TO THE BATTERY NEGATIVE. You should see some voltage (the actual amount is meaningful, nor specified) on each test, and the voltages should be about the same on each leg.

- finally, using your multi-meter and following the directions in the service manual, check the function of each of the 6 diodes in the rectifier to make sure the power is being properly rectified from AC to DC.

How do I know if my battery is good?:

Is it your battery, or your charging system, or something in-between?

The best way to know for sure is to use a multimeter (voltmeter) attached directly to your battery positive and negative terminals, and observe the following:

1) with the engine and all electrical accessories off, the battery should read a minimum of 12.8 volts DC. If not, the battery is either not fully charged, or it is bad (it is incapable of holding a full charge). Charge the battery fully and check again; if the reading is less than 12.8 volts, the battery is bad and should be replaced.

NOTE: most manuals describe checking the specific gravity of each battery cell electrolyte (fluid) as the preferred method of checking the condition of the battery. This reading should be between 1.2650 - 1.280 per cell. If a fully charged battery cannot reach these levels in all cells, then that cell is bad and the battery should be replaced.

2) If the first test above passes, leave the multimeter hooked up to the battery terminals, and press the starter button. While the starter is engaged (but before the bike starts), the battery voltage should be 9.5 volts or greater. If not, then this signals either a bad battery, very dirty or weak electrical connections, or it could be a incredibly problematic starter motor (not likely; it's probably the battery!).

3) if you run into this specific problem:

* "There were a few times when I cranked it, that it ALMOST started. It would start to fire immediately as I let off the start button. But it just wouldn't catch.

Then this is a symptom of a weak battery, due to any number of causes.......

What happens is that as the starter is being engaged, it gobbles up battery voltage. As soon as the start button is released, you now have full battery voltage available TO THE IGNITION CIRCUIT (including the pick-ups, the TCI, and especially the coils), and in that instant when you release the starter button, the coils get enough voltage to produce an adequate spark while the motor is still (by inertia) turning over. If everything is in a great state of tune, the bike will normally kick over. If not, you get the "almost fires" situation explained above, so.........

Test the battery voltage WHILE THE STARTER IS ENGAGED (a voltmeter across the + and - terminals of the battery is all that's needed). It should remain above 9.5 volts while the starter motor is engaged but without the engine running. If it drops below that level while the starter is active, then that's the "problem", and the cause of that problem must be determined and remedied (usually a sign of a bad battery, or it could be a incredibly problematic starter motor).

4) Your charging system output VOLTAGE should be checked, again at the battery terminals, while the engine is running. The measured voltage should be:

* 14.2 - 14.8 Volts at about 2,000 rpms for all non-X models, and the same voltage for "X" models, but at about 3,000 rpms. Again, you would measure these voltages at the battery terminals with your voltmeter.

NOTE: If your alternator is outputting more than 14.8 volts to the battery, your regulator-rectifier unit is bad and should be replaced. Over-charging a battery will quickly ruin it, and may cause severe damage or failure of other electrical components, such as the TCI or the computer monitor system (on bikes so equipped).

Here's your cheat sheet on all of the above:

Static Battery Voltage Test

Prior to conducting this test, make sure the battery has not been
recently charged. You must wait at least one hour after charging
your battery to conduct this test.

a) Adjust voltmeter to DC volts (20 volt range).
b) Place voltmeter leads to the battery terminals (positive to positive and negative to negative).
c) Read voltage and refer to the chart below.

State of Charge:

100% Charged with Sulfate Stop:
Using a syringe Hydrometer: 1.280
Using a Digital Voltmeter: 12.80 volts
Using a Floating-Ball Hydrometer: 5 balls floating

100% Charged:
Using a syringe Hydrometer: 1.265
Using a Digital Voltmeter: 12.60 volts
Using a Floating-Ball Hydrometer: 4 balls floating

75% Charged:
Using a syringe Hydrometer: 1.210
Using a Digital Voltmeter: 12.40 volts
Using a Floating-Ball Hydrometer: 3 balls floating

50% Charged:
Using a syringe Hydrometer: 1.160
Using a Digital Voltmeter: 12.10 volts
Using a Floating-Ball Hydrometer: 2 balls floating

25% Charged:
Using a syringe Hydrometer: 1.120
Using a Digital Voltmeter: 11.90 volts
Using a Floating-Ball Hydrometer: 1 ball floating

0% Charged:
Using a syringe Hydrometer: less than 1.100
Using a Digital Voltmeter: less than 11.80 volts
Using a Floating-Ball Hydrometer: 0 balls floating

Starting Load Test:

a) Adjust voltmeter to DC volts (20 volt range).
b) Place voltmeter leads to the battery terminals (positive to positive and negative to negative) .
c) Watch the voltmeter as you start your motorcycle, but before the engine is running.
d) If the voltage drops below 9.5 volts, the battery has very low capacity and should be replaced.

Charging System Tests:

a) Adjust voltmeter to DC volts (20 volt range).
b) Place voltmeter leads to the battery terminals (positive to positive and negative to negative).
c) Start the engine.
d) Bring engine up to approximately 2,500 rpm's.
e) Compare the voltage reading to the specification given below:

For all XJ-series models, the maximum available charging output VOLTAGE should be as follows (all values are approximate):

* approximately 500-2000 rpms: 1.8 volts gradually increasing to 14.2 volts
* 2000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts (all models except XJ700-X and XJ750-X)
* 3000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts (all XJ700-X and XJ750-X)

If your charging voltages are too low, suspect the alternator brushes first, then perform the alternator stator and rotor checks as described in the Alternator Section.

If your charging voltages are too high, suspect your Regulator - Rectifier unit first, and perhaps dirty or corroded electrical terminals. The procedure for checking these is too detailed to describe here, and you should consult your service manual for additional details.

5) Check the condition of your main circuit terminals.....they should be zestfully clean and uncorroded, or you're primed for a variety of problems......not only will your circuits not be getting full power out of your battery, but to add insult to injury, your charging system may think that the battery needs more juice, and so it starts cranking out amps like there's no tomorrow. It's pretty safe to say that neither of those two occurrences qualify as a Good Thing (tm), so...........start at the beginning, and inspect and clean (and then protect, like with di-electric grease or equivalent) all the [/b] terminal connection points[/b]:

* the positive battery post connection to the positive battery cable.
* the positive battery cable connection to the starter relay (or "solenoid").
* the main harness terminal connector from the starter relay.
* the main lead from the starter relay to the starter motor (both ends).
* the "main fuse" contacts inside the fusebox.
* the battery ground cable contacts at both the engine case and at the negative battery post (poor ground are just as bad as poor positive feeds; after all, it takes two to tango, or to complete a circuit, and electricity doesn't care where the restriction occurs).

Checking Alternator Stators:

Measure the resistance across each pair (white1 to white2, white1 to white3, and white2 to white3) of the three white wires (white1, white2, and white3) at the connector; the specifications should be:

0.50 ohms +/- 10% for all XJ550 models.

0.46 ohms +/- 10% for all XJ650, all XJ700, all XJ750, and XJ900RK models.

0.37 ohms +/- 10% for all XJ1100 models.

0.40 ohms +/- 10% for all XS1100 models.

Note that the resistance specifications for the stators are extremely small; they should barely have any resistance at all (compared to most other electrical devices).

Checking Alternator Rotors:

Measure the resistance across the two lead wires (usually brown and green) at the connector; the specifications should be:.

4.5 ohms +/- 10% for all XJ550 models.

4.0 ohms +/- 10% for all XJ650, all XJ700, all XJ750, XJ900RK, and XJ1100 models.

3.5 ohms +/- 10% for all XS1100 models (field coil).

Note that worn, dirty, or damaged alternator brushes can affect these readings, as can "dirty" copper commutator rings on the rotor face (where the brushes contact the rotor):


Checking Voltage Drops in Wire Circuits:

This information is really important, and you should take the time to understand it.


Wiring Diagrams:

MiCarl's wiring diagrams: note that some of these diagrams are for Euro bikes, which may be a bit different than North American bikes. Also beware: factory wire diagrams do have errors in them.


Here’s a good source of info on how to actually read a wiring schematic:


Another good source for wiring diagrams can be found at:

NOTE: some of these may be for non-US models.

1981-3 XJ550 Maxim WIRING DIAGRAM

1981-83 XJ550 Seca WIRING DIAGRAM

The World’s Greatest XJ550 Seca Wiring Diagram:

1980-82 XJ650 Maxim, Midnight Maxim, and Seca WIRING DIAGRAM




1982-83 XJ750 Seca WIRING DIAGRAM



Components Key Guide for all of the above WIRING DIAGRAM


Return to Top of Page