81 Midnight Special rectifier diode

[FJ111200]

I was chasing a bad mis-fire and during my investigations came across this rectifier diode which had broken loose from the solder attached to the bullet connector holding it in the loom.
I used an old one I found from an old FJ model and it cured the problem, but what I want to know is if it can be left out of the loom altogether and not used.
I know I could go outside and remove it and try but if anyone knows already I would be grateful. Thanks.
Sorry what I should have also said was, just join the bullet connectors in the loom to eliminate the rectifier diode.

[3Phase]

The harness diode runs the headlight relay.

You can ditch the diode if you get rid of the headlight relay and jumper the wires at the relay harness connector: Red/Yellow to Blue/Black.


TL;DR

1980 and 1981 headlight relay wires:
Red/Yellow is 12V in from the 10A Head fuse.
Blue/Black is 12V out to the RLU.
White is +DC from one alternator stator coil.
Black is ground.

After the engine starts and the alternator is working, the harness diode feeds +DC pulses from one leg of the stator through the White wire to the headlight relay coil and turns it on.

The relay has an internal latch diode connecting the Blue/Black wire terminal to the White wire terminal so the relay stays on. The relay won't chatter and make the headlight flicker at low RPM and it won't turn off until the ignition is switched off.

Once latched, the harness diode blocks 12V DC from feeding back into the stator and the rectifier from the 10A Head circuit.

[FJ111200]

Thanks for the reply.
So it's got nothing to do with making my bike mis-fire?
It seems strange that I've been looking for this mis-firing problem and then when I find this broken diode connector and swap for another the mis-fire goes away.

[3Phase]

You're a little far away for me to look over the harness.

No, by itself a broken or open-circuit diode wouldn't cause misfiring, the headlight just wouldn't turn on when the alternator sparks up with the engine.

If the diode was shorted and one of its connectors broke when you dug into the harness then, yes, it might have caused misfiring.
A shorted diode will allow the 10A Head circuit to drive the stator and rectifier as loads in addition to the lights.

Check the old diode with an Ohm meter or a test light to see if it acts like a diode and only conducts current in one direction, if it's blown/open-circuit, or if it's shorted and turned into a fancy piece of wire with a ceramic blob in the middle.

[FJ111200]

Ah, I've just remembered something, probably important regarding the headlight, sorry for this.
I bought the bike secondhand off a member on the UK forum, and someone, don't know if it was him but he had allsorts written on bits of paper regarding switches, wires and the like, has wired in a UK spec right hand lighting/start button/stop switch which means the headlight doesn't come on when the ignition switch is turned on, so basically the headlight and tail light can be switched on and off at will.
Now what does that tell you? Sorry for not adding that in my first post.

[3Phase]

Heh, you need to find the merry 'wit that wired it and ask him what he did!

I can think of several ways to change the wiring, from using a right-hand handlebar switch with the headlight relay like the one that came on the US model '78E, to other, less savory, options.

[FJ111200]

Thanks for all your help.
Merry 'wit? Is that a bit like a gibbon?

[3Phase]

Thanks for all your help.
Merry 'wit? Is that a bit like a gibbon?

It's a 'amily-'riendly 'orum, of course it's a gibbon.