Charging issue - won’t charge with headlight on

markaust18 · Aug 11, 2024

Hi all,
I have a charging issue with my Mk 2 Commando. It has a Pazon ignition, new 3 phase alternator, new rotor, new Wassell regulator rectifier. It charges 13.7-9 volts when running without the headlights on, but when I turn the lights on it will not charge at all.
I’m stumped, any ideas what I should be looking for?
Thanks for the help.

Mart UK · Aug 11, 2024

What voltage at what revs? I doubt my Mk3 is charging at tickover, but fine once I'm riding.

Your title says not starting with the headlights on. If that's the case, some EIs require a min voltage to trigger. I'd suspect you battery giving up under load, even if it appears charged before switching on?

kommando · Aug 11, 2024

I dumped my Wassell regulator rectifier as it had a current draw that would drain a battery in 2 days with the ignition turned off. Likely not your issue but I would not trust it not to have other faults.

markaust18 · Aug 11, 2024

Mart UK said:
What voltage at what revs? I doubt my Mk3 is charging at tickover, but fine once I'm riding.

With the light on, it is 12.2 volts at 3,000 ish

kommando · Aug 11, 2024

You either have a 100W bulb or the alternator output is down. Do you get voltage on all three legs of the 3 phase alternator. Set the meter to AC volts not DC and probe the 3 connections.

marshg246 · Aug 11, 2024

kommando said:
You either have a 100W bulb or the alternator output is down. Do you get voltage on all three legs of the 3 phase alternator. Set the meter to AC volts not DC and probe the 3 connections.

Also a bad master switch, bad connection of the Blue/Yellow at the master switch, bad connections along the way to the headlight switch, bad headlight switch, bad connections to the handlebar console Blue or Blue/White or Blue/Red, or bad connection to the bulb. In other words, a bad connection involving the headlight can increase the required current to more than the alternator can overcome, especially if the battery is weak. You can eliminate some of that by trying with the headlight on high or low beam - if OK on one but not the other, then the problem is in the handlebar console or the connection from the handlebar console to the bulb socket or the bulb socket itself.

If you check the Blue wire from the headlight switch to the handlebar console Blue wire it should be identical to the battery voltage at all times/RPMs. If that is the case then check the Blue/White (high beam) and Blue/Red as the connection to the headlight bulb connector. Whichever is selected should be identical to the battery voltage at all times. From those checks you can determine if there are any bad connections related to the headlight.

To understand these tests better, see: https://www.gregmarsh.com/MC/ViewPDF.aspx?key=uvd

dobba99 · Aug 11, 2024

Does the bike still have the original wiring harness? if so it will be past its best by now, corroded terminals, blackwire corrosion along the copper wires under the insulation etc etc, has the switchgear been serviced? the internals corrode as well.
Follow Al Osborns testing regime (to be found on his website @ aoservices.co.uk look under the info sheets tab)

markaust18 · Aug 11, 2024

marshg246 said:
Also a bad master switch, bad connection of the Blue/Yellow at the master switch, bad connections along the way to the headlight switch, bad headlight switch, bad connections to the handlebar console Blue or Blue/White or Blue/Red, or bad connection to the bulb. In other words, a bad connection involving the headlight can increase the required current to more than the alternator can overcome, especially if the battery is weak. You can eliminate some of that by trying with the headlight on high or low beam - if OK on one but not the other, then the problem is in the handlebar console or the connection from the handlebar console to the bulb socket or the bulb socket itself.

If you check the Blue wire from the headlight switch to the handlebar console Blue wire it should be identical to the battery voltage at all times/RPMs. If that is the case then check the Blue/White (high beam) and Blue/Red as the connection to the headlight bulb connector. Whichever is selected should be identical to the battery voltage at all times. From those checks you can determine if there are any bad connections related to the headlight.

To understand these tests better, see: https://www.gregmarsh.com/MC/ViewPDF.aspx?key=uvd

Thanks I’ll check all that out, it’s the same on high and low beam.

markaust18 · Aug 11, 2024

dobba99 said:
Does the bike still have the original wiring harness? if so it will be past its best by now, corroded terminals, blackwire corrosion along the copper wires under the insulation etc etc, has the switchgear been serviced? the internals corrode as well.
Follow Al Osborns testing regime (to be found on his website @ aoservices.co.uk look under the info sheets tab)

It was rewired some time ago with negative earth. I’ll check out that sight, thanks for the tip

MexicoMike · Aug 11, 2024

"Follow Al Osborns testing regime (to be found on his website @ aoservices.co.uk look under the info sheets tab)"

FWIW, I had never seen that seen that site...Great Stuff!!! Thanks for posting it in your response to markaust18!!

"

dobba99 · Aug 12, 2024

MexicoMike said:
"Follow Al Osborns testing regime (to be found on his website @ aoservices.co.uk look under the info sheets tab)"

FWIW, I had never seen that seen that site...Great Stuff!!! Thanks for posting it in your response to markaust18!!

"

Maybe LAB can add it to the technical pages,

Charging issue - won’t charge with headlight on

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