I wonder if anyone can help with a problem I have. I’m rebuilding a 750 Commando and have re-wired it to the 1972 diagram. It has the original Lucas handlebar switches which I have stripped and cleaned contacts and checked for correct switching with a meter.
I bought a high power dual polarity pre-focus LED headlight bulb from Paul Goff but when fitted only get main beam wether or not I’m on dip or main also the main beam warning light did not come on.
I have a good quality Fluke meter so checked that I was only getting power to the correct contact lead at the headlight for main and dip and none at the lead when the other one was switched. I also checked the bulb with a battery off the bike to prove that it had a working dip and main beam and which contact on the bulb was which and that it matched the bulb holder leads, all o.k. I don’t know why but I removed the main beam warning bulb and then I had main beam and dip beam as it should be.
I contacted Paul who was very helpful and sent me a diode to put in the main beam warning supply lead, still no change. He then sent me an LED main beam warning bulb also FOC but again no change.
If I put a standard bulb in everything works as it should but with the LED bulb it only works with the warning light removed.
I am happy without a main beam warning light but its just got to the point that I would love to know what the problem is out of curiosity.
Alternatively can anyone recommend a good normal filament bulb to use.
Bike is positive earth as original.
Hope someone can shed some light on this ( sorry!!! ).
Not idea what a pre focus bulb is so can,t recommend a decent filament type but my H4 setup has relays for dip and high beam with a blue LED warning light in the console.
When changing from the Osram Nightbreaker Laser H4 to a £9 plug and play El Cheapo LED replacement, everything worked exactly the same. Better headlight and no extra diodes needed on my standard positive earth system. Apparently most H4 LED bulbs of this type are dual polarity, your pre focus LED may have a fault. Have you tried a replacement?
Look in depth at the Earth connection for the Main Beam Warning. Try removing/disconnecting the
Earth to the lamp, if with this off then I would suspect there is poor earth to the warning lamp.
Report back or phone.. AO
I have further information on this problem. Not an answer yet but we are working on it.
Sorry for late response and thank you for your help. Tried many different ways around this problem and Al has been very helpful too.
Interesting that you have relays in your headlamp circuits, I’ll have two investigate this, might make a difference.
We have a result to the above problem, which is LED headlamp has both beams on if you try to use a traditional Main beam warning lamp. Without the main beam warning lamp the LED headlamp and dip switch works as intended. Not an earth fault, perhaps not an LED bulb problem but certainly an issue. Finally cured by using a relay to switch the main beam on (from the dip switch) while connecting the Main Beam Warning light to the output of the dip switch (and input to operate the relay).
If anyone else gets such a problem then please get in touch aoservices.co.uk or NOC Electrical advice.
PS Cheers Phil for persevering.
hopefully your headlight working normally now. I,ve always used relays on horns and headlights on my bikes. Most cars have them as standard, being the best bet tor bright lights and loud horns with reduced load on our Lucas ignition switch
The headlight relays are standard off the shelf 12v type taped together and tucked in the headlight shell behind the reflector since 2007. The waterproof horn relay controlling twin horns, is mounted on the frame tube above the exhaust rocker covers in the weather, heat and vibration. All the relay connections are soldered to the spade connectors with heat shrink tubing support and separate earths from a master wire to the battery, not relying on the frame earth although this is still present
Out of interest my bike relays have always been reliable over high mileages despite more exposed and challenging working conditions than the protected relay boxes in cars. My two vintage high mileage Audis have had many relay changes from fuel pump to windows. I won,t even mention the troublesome engine management and turbo sensors on one, but the old mechanical fuel injection on the other still works perfectly after nearly 200k miles
Once again many thanks for persevering with me!
All properly wired up now and mini relay fits easily in the back of the headlamp shell. Have at last managed to fit the headlamp to the shell for good!
All the best,
Many thanks for your interest in this problem. I could have ridden the bike without a warning light, although probably not strictly legal, but curiosity to find a fix got the better of me and with Al Osborn’s help I was able to close the door on that one!!