No Headlight

Hi,

1975 850 mk3. It is an import back to the UK, but the ignition switch works like a UK model, ignition only on 1st clockwise key position, ignition and lights next step round. I don't know if i have UK switches: headlight/pilot slider on righthand handlebar switchgear; the Hi/Lo mainbeam slider and horn button are on the left bar switchgear.

First proper routine check of the year. No headlamp, nor main beam. Pilot works OK. The wiring in the headlamp is in good condition. The bulb (halogen) looks OK. I still get pilot only when the righthand handlebar switch is set to headlight and no main beam when I move the lefthand handlebar switch to 'Hi' (also, no blue tell-tale light in the console). However, the main beam does light up with the flasher mode on the horn button, along with the blue tell-tale.

Is this likely to be the right hand switch (the head/pilot slider)? If so, on the left side switchgear, why does the Hi/Lo button not work when the flasher button does?
p.s. The starter button on the right side is still working fine.

Mart UK said:

If so, on the left side switchgear, why does the Hi/Lo button not work when the flasher button does?

Click to expand...

Because the headlamp flasher circuit is powered by white and not the headlamp circuit.

Mart UK said:

1975 850 mk3. It is an import back to the UK, but the ignition switch works like a UK model, ignition only on 1st clockwise key position, ignition and lights next step round. I don't know if i have UK switches: headlight/pilot slider on righthand handlebar switchgear; the Hi/Lo mainbeam slider and horn button are on the left bar switchgear.

Click to expand...

Unless it came back from Canada then it should be the same.

L.A.B. said:

Unless it came back from Canada then it should be the same.

Click to expand...

Yes, c/w position 1 is no lights. Which market though, I don't know. From the restoration photos on file, it was rusty enough. Certainly not a Southern state! And, in any event, it could have been UK-ised when stuff was replaced.

To check the headlamp circuit, there should be a blue/yellow on terminal 4 of the ignition switch. This goes to the pilot/head switch on the right-hand cluster. When the head position is selected, power goes to the left-hand cluster through a blue wire, where it passes to either blue/white for the main beam or blue/red for the dip beam.

If it was a Canadian model then the pilot/head switch was bypassed so that it was not possible to extinguish the headlamp. If the ignition switch works as you have described then it seems unlikely to be a Canadian model.

The section of wire to the left-hand switch cluster from the plug may also be blue/yellow so the wire colour changes back to blue/yellow from blue.

Mart UK said:

I still get pilot only when the righthand handlebar switch is set to headlight

Click to expand...

The pilot light as well as the tail lamp and instruments are powered by the brown/green from terminal 3 of the ignition switch.
The right-hand switch only powers the headlamp so the pilot is on regardless of the R/H switch position. There's no connection between the RH switch and the pilot light.

L.A.B. said:

To check the headlamp circuit, there should be a blue/yellow on terminal 4 of the ignition switch. This goes to the pilot/head switch on the right-hand cluster. When the head position is selected, power goes to the left-hand cluster through a blue wire, where it passes to either blue/white for the main beam or blue/red for the dip beam.

If it was a Canadian model then the pilot/head switch was bypassed so that it was not possible to extinguish the headlamp. If the ignition switch works as you have described then it seems unlikely to be a Canadian model.

Click to expand...

Thank you. That helps. Yes, I have blue / white and blue / red (+ black) on the light socket in the headlamp bowl. So, it could be one of 3 switches, or the wiring between them:
Switches:
- no power getting to T4 pin from the key switch position;
- the contact in the headlight slide switch in the RH cluster; or
- seems unlikely, no contact in both sides of the Hi/Lo slider in the LH cluster
I have a 12v static timing light. Can I check each of the switches by turning on the ignition (2nd position) connecting one side of the timing light to the relevant switch's terminal and the other side to earth? If it lights, it's powering up.

Wiring:
I think I can check the wiring's OK with 4 tests. Should I have continuity between:
1. Bl/Y at ignition switch and Bl/Y RH cluster;
2. Blue RH to LH (possibly Bl/Y on LHS) clusters; then
3. Bl/W at left cluster and headlight socket in the headlamp bowl; and
4. Bl/R at left cluster and headlight socket in the headlamp bowl?

Thanks, Martin

L.A.B. said:

Because the headlamp flasher circuit is powered by white and not the headlamp circuit.

Click to expand...

I don't have a White on the headlight socket, just blue / white for mainbeam. So I guess the white connects into the Bl/W somewhere in the headlamp bowl?

Mart UK said:

I don't have a White on the headlight socket

Click to expand...

Correct. The headlamp is powered by blue/white (main) or blue/red (dip) from blue/yellow and blue.

The headlamp flasher button connects white to blue/white so blue/white has two separate feeds from the LH switch cluster.

L.A.B. said:

The headlamp flasher button connects white to blue/white.

Click to expand...

Still trying to get my head round it. But it seems the failure must be earlier in the blue/white circuit, before the point of the white to blue/white connection, as the blue whit has continuity to the bulb from that point. Can't picture how that horn button works at the moment. I'll have a look tomorrow, sure it will make sense then.

Thanks for the help.

Pushing the button up connects white to the blue/white on the top of the switch which is broken off in the picture. The other headlamp wires are in the other half of the switch which also has a blue/white wire.

Thank you Les. Turned out quite simple. T4 on the ignition switch was live. I had no continuity from there to Bl/Y in the handlebar switch. Tracing back from the bar switch to the headlamp bowl, the switch wires connect with bullets and, hidden, both headlight switch bullets were just dangling free. I popped them back in, + gave the females the lightest of crimps and all works lovely now.