View Full Version : Ironhead generaor specs

13th April 2010, 03:07
I have a charging issue with my 79 sporty, what shuld the voltage readings be on the 2 terminals of the generator? I have only 3 vlts from the "f" terminal when running. is this right? ther is 12+ from the other terminal when running but only 11 out of the regulators red wire to the battery. help.....

Fe Head
13th April 2010, 03:28
Welcome "randr1774" to the XL Forum and to the ever growing group of Ironhead owners - not to mention the special 1979 flavour.

The most comprehensive overview of the 1979's model 65A 12 volt generator is found in the Red Technical Sticky section found at the top of this forum's opening page along with a sizable gaggle of other valuble topics.

I have the "Charging System Checkout" one posted as a linlk here for you to click on.


In addition below is a previous reply I provided to a fellow member who shared similar concerns a few weeks ago.

The full 65A HD DC generator voltage testing protocol to follow is provided here below.

To test the VOLTAGE out and show that the field windings are good - perform the following.

1. With the generator mounted on the motorcycle or test drive stand and no wires connected to the “A” and “F” terminals, connect the red lead from a voltage meter to the “A” terminal.

2. Connect the black lead to a good clean ground.

3. Set the meter to 20 VDC scale and accelerate to spin the generator shaft at 3000 RPM.

The generator turns faster than the engine, on Sportster,1.3 times the engine's rpm, so on the Sportsters a 2500 tach RPM = 3000 rpm generator speed.

The voltage meter should read a positive 2-4 volts DC.

If you get no voltage or a negative voltage, polarize the generator. (See Polarize in red sticky section) Reversed voltage will be cured by proper polarizing.

4. After obtaining a reading of 2-4 volts positive on the meter leave the meter hooked-up the same and change to a 50 DC volt scale.

Use a jumper wire and connect the “F” terminal to ground just long enough to read the meter. It should read a positive 40-50 volts.

These results will show that with an open field circuit you have low voltage AND with a closed field circuit the voltage is high.

It is the regulator's sole job to keep the voltage at the proper level typicaly ~13.5 volts and limit the current output.

With the diode working inside the headlight bucket (may need a new one ~ $1.00 at Radio Shack P/N 1N4001) so the GEN light goes OFF when the engine is at or above 1000 RPMs and with the correct output voltages you should be up and running.

If not then it's time to dismantle at least the left side/end of the generator and check/clean or replace the brushes along with re-grooving the mica separations between the copper commutator strips.


P.S. Always be sure to add some more viscous wheel bearing type grease to the outboard needle bearing before re-assembling the end cap.

Having only 11 volts coming from the regulator suggests the Solid State Regulator is not doing its job properly and may not be grounded securely. The base of the regulator AND the frame mountings need to be squeeky or shiny clean and if possible have some dielectric gease placed over both contacting surfaces before re-bolting them together.

If the corrosion gets started it can cause the Regulator/Rectifier to over heat and gradually fail as shown when the red GEN light stays on above the engine's 1000 RPM level. Even the male and female sides of the connection plug should be dielectrically coated as well to keep the salt/moisture out.

You will also need to purchase a FM or factory manual and Service/Parts Manual as these will provide quick insight into most aspects of the bike and become a handy reference when identifying various components or their specifications.

All the best as you become one with your own machine.


13th April 2010, 03:36
Thank you!!!