Boxerworks.com

Hi folks,

I’m trying to understand and fix an electrical problem.

My ‘72 r60/5 seems to have working switches and lights but...

When the headlights are turned on the brake light turns on. It stays bright and unchanged even if the brake lever or pedal is pressed.

When the key is in, but the headlights are off, the brake light responds normally to the lever and pedal.

The high beams work normally as well.

I read in another post that the headlight and tail light are receiving power in parallel instead of series. And that a ground wire may have been reversed.

Any help would be appreciated,
Ty Andrew

Unless there has been some fairly major interference with the wiring, this has got to be something to do with the connections at the rear lamp cluster.

Yopu don't say what is happening with the rear light (as opposed to the brake light)... Is it coming on with the front marker lamp (sidelight... parking light... whatever you call it).

In any case, I think you need to take the rear lamp out of the housing and see exactly what is happening. It will probably be a srongly connected, disconnected or shorted wire at the connectors. A meter to check the various connections would be very useful. FWIW, there should be three wires copnnecting to the rear lamp cluster...

Brown - ground - should always have connectivity to the frame earth and to battery negative.

Grey/black - rear light feed - should be at battery voltage when the position lights are on and when the headlights are on. Otherwise it should show 0 volts

Green/Red - Brake light feed - should be at battery voltage when either the rear brake light switch or the front brake light switch (if fitted) is actuated otherwise it should show 0 volts.

Check the condition of the wires and the condition of the bulb holder. Also, try another bulb. It's not unknown for the filaments in a bulb to short out internally so the wrong filament comes on.

Rob

Ty Rob,

I’ll start there.

About “the rear light as opposed to the brake light”, when the nail key is swung to the headlight or parking position, the brake light is on. It’s bright. When the nail key is in but straight, both the brake lever and pedal, when pressed, turn on the running light. Noticeably dimmer.

Ah, then the obvious suspect is the connections at the rear light cluster with the Grey/Black and the Green/Red being swapped. However, do try a different bulb... I've seen occasions where the connections on the base of the bulb have been soldered backwards...

If that doesn't help, can you tell us a bit about the history of the problem... is this a new (to you) bike? Has the problem occured recently? Does it co-incide with any work on the bike? anything like that.

Rob

I wish I could send a photo, Rob. The rear light cluster has a clean, corrosion free, socket base, bulb, and connections. Both filaments are intact. No obvious tool marks or fresh scratching on the clipped wire connectors.

The socket has one grey/black (left side) and one green/red wires, each soldered to the conductor that touches the bulb. The socket base also has two ground wires, one is soldered and the other is a clipped connector.

To the left side of the socket base is another wire block made up of two soldered and two clipped connectors all with blue/red stripe wire.

Could the grey/black and green/red have been reversed in another location?

History: I have owned this bike for 35 years. It was my first bike. It has relatively low miles and runs well. This summer it went to a local mechanic for basic service, new bars, new seat, new tires, a new horn, and new paint on the tank and fenders.

Ty again for your help,
Andrew

I didn’t notice the problem with the brake lights until the day after it came back from service for the second time. I returned the bike initially after service because the cable routing was tight after the bar change.

I noticed one more detail:

When the headlight is turned on the brake light comes on. At the same time, the brake lever and brake pedal action turns the rear/running light on/off.

So, both filaments are lighting at the same time.

And I can also add to the recent history:

The bike was stored outside with the shops nail key in it. I noticed a faint mud ring around the extended position of the plastic slider when I got it home.

Perhaps a short has formed from rust/corrosion in the ignition switch?

I also incorrectly described the colors of the 4 blue wires connected to the block to the left of the bulb socket. One pair is blue/red stripe and the other pair is blue/black stripe.

Measuring voltage from battery terminals to wires in rear light fixture.

Battery voltage 11.26v

(Turning headlight on turns on brake light.
And applying the brakes turns on the rear/running light.

1)Key in, headlight off, no brakes:

From negative battery terminal to

Grey/black 7.6mv
Green/red 7.6mv
Brown 7.6mv

Blue/black 7.6mv
Blue/red 7.6mv

From positive battery terminal to

Grey/black 11.61v
Green/red 11.61v
Brown 11.61v

Blue/black 11.61v
Blue/red 11.61v

2)Key in, headlight off, brakes applied:

From negative battery terminal to

Grey/black 50mv
Green/red 10.39v
Brown 26.7mv

Blue/black 22mv
Blue/red 22mv

From positive battery terminal to

Grey/black 11.48v
Green/red 1v
Brown 11.55v

Blue/black 11.52v
Blue/red 11.52v

3)Key in, headlight on, no brakes:

From negative battery terminal to

Grey/black 10.74v
Green/red 0.48v
Brown 143mv

Blue/black 155.9mv
Blue/red 155.9mv

From positive battery terminal to

Grey/black 0.49v
Green/red 10.79v
Brown 10.96v

Blue/black 10.94v
Blue/red 10.94v

4)Key in, headlight on, brakes on:

From negative battery terminal to

Grey/black 10.47v
Green/red 9.71v
Brown 170mv

Blue/black 170mv
Blue/red 170mv

From positive battery terminal to

Grey/black 0.5v
Green/red 385mv
Brown 10.55v

Blue/black 10.55v
Blue/red 10.55v