Lights staying on. 1977 R100/7

[Stilbo]

Hello.
New to this forum but this is my fourth Airhead over the last forty years...
Got out for a ride today, pulled into my shop, turned the key off and headlight and taillight stayed on.
Cycled the ignition and light switch off and on.
Still stays on.
Disconnected battery ground and reconnected the ground and lights still staying on....
Has anyone experienced this on an /7?
Thanks!

[gspd]

Sounds like a stuck relay....
Assuming your bike still has stock electricals....
one at a time, pull out every relay you can locate (in the headlight shell or under the gas tank) until you find the culprit.

[ME 109]

Sounds like a stuck relay....
Assuming your bike still has stock electricals....
one at a time, pull out every relay you can locate (in the headlight shell or under the gas tank) until you find the culprit.

I thought relay, but then does the tail light get power from the headlight relay too?
What about the horn, does it work with the ignition off?

[Rob Frankham]

Sounds like a stuck relay....
Assuming your bike still has stock electricals....
one at a time, pull out every relay you can locate (in the headlight shell or under the gas tank) until you find the culprit.

I thought relay, but then does the tail light get power from the headlight relay too?

Yes, it does. the pilot light circuit which controls the pilot light, the tail light and the instrument lights gets its power from on of two (three in euro spec bikes) sources.

The horn is a different circuit and isn't affected.

On US spec bikes, this circuit (which is characterised by wires with a grey main colour) gets it's power from the ignition switch when (and only when) this is in the parking light position but once the ignition switch is set to run, the lights get their power from the relay via a seperate 87b output connection amd the contact in the ignition switch is disconnected. To make things interesting, many wiring diagrams label the 87b terminal on the relay as 87a which makes no sense and would mean that the pilot light circuit is off when it should be on (and vice versa).

On euro spec bikes, which have an independent light switch on the handlebars. When the pilot light circuit is on without the headlights, the power for the pilot light circuit is derived from the handlebar lighting switch as the relay isn't activated.

Just to add icing to the simnal cake (it being Easter and all) there is another arrangement used on 'Gs models and the R45/65 series where the ignition switch has 5 positions, the pilot light and headlight being switched from the ignition switch. In this case, the system is much simpler, the pilto light power always comes from the ignition switch.

Finally, the above applies to models from MY75 to MY84. /5 machines, early /6 and monoshock models all have different variations. No one said it would be simple...

Rob