Honda-SOHC

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Charging System Checking on SOHC4s


All of our bikes are now getting old and electrical problems are the most common problem encountered.

This is, I hope, meant to be a relatively easy way to test and diagnose which element is likely to be faulty.

Firstly let me say since starting work at a dealer in 1974(ish) I have NEVER seen an electrically faulty field coil or stator; I have seen them physically damaged by traffic accident or being dropped. Whilst doing all tests at connectors check for melting plastic, burning, blackening or loose fit.

Testing equipment required is a multimeter that can read both AC and DC volts plus resistance. You will also need a fully charged battery installed correctly.

OK start by turning off the kill switch and disconnecting the headlamp and tail light, especially on US models where lights come on with ignition. Also disconnect the 3 wires at the voltage regulator.

Set multimeter to DC volts scale of 20
Firmly connect the  red lead to +ve post on the battery and then use the black lead to check and note battery voltage at –ve post; move the black lead to the engine end of ground lead and re-check the voltage If there is any variation, the ground lead needs cleaning/tightening/replacing.

Now firmly connect the black lead to the battery –ve and using the red lead, check and compare the voltage at the solenoid connection, then the main fuse in, main fuse out and the red wire at the ignition switch.

If at any one point the voltage falls by more than a fraction of a volt there is a bad wire or connection between the point being tested and previous test point and this needs to be rectified.

Turn the ignition switch on and check the voltage at the black wire (switched 12V). Again there should ideally be NO voltage drop (a small fraction is permissible). Go to the black connectors in the headlamp shell and finally to the black wire at voltage regulator.

The MAXIMUM voltage drop between battery and regulator should be less than 0.5V (preferably less).

Connect just the black wire to the regulator and measure the voltage at the white connector on the regulator, reconnect the white wire to the regulator and check the voltage at the white field connector just outside generator case.

Reconnect all wires disconnected to test voltages but not the lights.

The next test gets a bit more difficult as you need to disconnect the block connector that goes to the generator but re connect the green and white wires that go to the field coil; this also means that the oil and neutral light won’t work. On the 750 you can disconnect the wires just outside the generator cover and leave the block connector alone.

Remove your multimeter from battery and reset to AC volts of about 100.

Start the engine then if you look at the block connector from generator there are 3 yellow wires which gives 3 “pairs” (Imagine wires labelled 1, 2 and 3 that makes 1-2, 1-3 & 2-3)

Test the AC voltage across the 3 pairs of wires. This should read between 15 and 60 depending on revs.

There is a testing procedure in the Manual for rectifiers but you could say that if you have done all the tests above and get the ac voltage above but no charge at battery the rectifier or it’s wiring is suspect

Bryan Jones May 2020

Lazy I know but Menno’s exquisite sidepanel will not come off with the normal amount of force.  Probably down to the new rubbers.

I can’t reach the positive terminal to charge the battery.

Where else could I connect it that’s accessible in a crowded garage.


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This is a bit more complicated than I thought at first...

Anyone seeing this problm please report back here with the version of iOS or Android that they are using.

Me: iOS 13.3