Brake running light

[collinsra]

Hello everyone,

Having a new issue on my 1977 GS550. I recently noticed that the running light for my tail light is not working. Using the wiring diagram, it seems that the running light is the brown wire running to the rear. Using a multimeter, there is zero voltage coming from the wire. ALL other lights work as intended.

Opening the headlight, I see two brown wires together in a double-female bullet connector with nothing connected to it. There is about 4.5v coming from these wires...not sure how much should be coming to this.

The only definitive solution I see right now is to completely rip apart the factory harness and follow this little brown wire to see where its going and its condition. Hoping not to have to do this, and hoping someone know where this wire leads...I cannot determine this from the wiring diagram.

All fuses are fine.

Anyone have any idea how to figure this out?

[collinsra]

So further review of the wiring diagram, and it seems that the brown wire goes into the ignition switch. Looking at my ignition switch, there is a brown wire, but the only one that gets 12v is the orange. When the connectors between the ignition switch and the harness are connected, there is still no power going to the brown wire....confused.

[Steve]

Power routing to the tail light via the brown wire is indeed strange.

At the ignition switch, the brown wire is fed by the gray wire when the switch is in the ON position. That gray wire is fed by the headlight circuit, exactly where it connects depends on your bike.

When the ignition switch is in the PARK position, the brown wire is fed by the red wire, meaning that it will be the only thing receiving power.

.

[qcktvr]

Good morning,
I had problems with my rear light having a mind of its own, quick fix was to splice wire (brown) to it into the wire feeding the license plate light in the tail end. This also prevents unintentionally leaving the rear light on with the steering locked and returning to a flat battery..
Regards

[hannibal]

When the ignition switch and headlight switch are both on, the grey wire sends power to the brown wire through the ignition switch and to the instrument cluster lights. Do you cluster lights work? If so, that would suggest your issues are either after the grey wire splits between the cluster and the ignition, the ignition switch itself, or after the brown wire leaves the ignition switch. I would work through it in that order.

I'm vaguely remember the empty brown connector in the headlight bucket but can't recall its purpose. Very strange that you're not seeing 12 volts there.

[Steve]

I'm vaguely remember the empty brown connector in the headlight bucket but can't recall its purpose. Very strange that you're not seeing 12 volts there.

Some models had running lights in the front turn signals. They would be powered by that brown wire.

.

[collinsra]

When the ignition switch and headlight switch are both on, the grey wire sends power to the brown wire through the ignition switch and to the instrument cluster lights. Do you cluster lights work? If so, that would suggest your issues are either after the grey wire splits between the cluster and the ignition, the ignition switch itself, or after the brown wire leaves the ignition switch. I would work through it in that order.

I'm vaguely remember the empty brown connector in the headlight bucket but can't recall its purpose. Very strange that you're not seeing 12 volts there.

Cluster lights all work. Every other light that should work does. To address a previous reply, if I splice the brown into the tail light, wouldn't that produce too much voltage and have the light on full power, vice being dimmer, then brighter when the brake is engaged?

Ill test a bit more and follow up. I greatly appreciate the replies.

[collinsra]

update: so the double female brown wire is getting 12v. And as previously recommended, I checked to see if the gray was feeding the brown when the switch was on, and it is.

so by deductive reasoning, the problem lies somewhere before headlight and after the tail light (yes, narrowed it down haha). Perhaps a short in that wire along the harness.

i plan to rewire the whole bike in the future, but for a temp fix, I'm thinking of just connecting the running light wire to another power source actuated by the headlight switch. So perhaps one rogue wire ran from the tail light to the cluster....a bit janky, I know. Thoughts?