rear brake light switch

whilst checking out the electrics on my mk2 lemans today i notice that the rear brake light will work even with the ignition of is this correct or have i discovered a problem :question:

Both front and rear brake light switches should have blue/red wires to the rear bulb both joined in the connector block in the headlamp shell. The rear switch is supplied via a blue wire from fuse F1 which is supplied via a brown wire from the ignition switch. This should not be live with the ignition off.

The front switch is supplied via a red wire that comes from the volt meter and other idiot lights this joins to a red/black wire in the other connector block in the headlamp shell. The red/black wire goes to fuse F3 which is also connected to the ignition switch via the same brown wire and also should not be live with the ignition off.

I would suspect that a rewire has been done. If the rear brake switch is connected to fuse F4, F5 or F6 it would be live even with the ignition off. Of course it could just be connected straight to the battery which would also display the same signs.

If you send me your email address via PM I can send you a pdf copy of my coloured wiring diagram for free, please confirm if the idiot lights are supplied by printed circuit board or are wired in to the loom. I also sell A3 laminated copies of my wiring diagrams but that would just seem like touting for business, which it isn’t because the day job pays a lot more! See here

Best wishes Chris

Ditto what Chris said.
They don’t usually work with the ignition off. Indicators do (so you can have Hazards working with the key out) but not the brake light or horn.

Thanks Chris the bike has not had a rewire only a new fuse box I will check that the switch is supplied from the correct fuse. I checked the front switch which is not live with ignition off

Both brake switches are off a blue wire, so shouldn’t be seperate however somewhere along the line a brown wire is involved, headlamp flasher possibly. Who put in the new fusebox?

Thinking about it, it’s possible rear brake switch blue wire is connected to one of the permanently live fuses, 5 or 6. Instead it should be on 1, 2, or 3.

According to the factory wiring diagram the front brake light switch is fed by a red wire. Carl Alison also shows this as well. Headlight flash is a brown feed from fuse F2.

Isn’t that what I said?

The rear brake light switch should be from fuse F1 this is fed by a brown wire from the ignition switch, see the wiring diagram I sent you.
Carl Allison’s one shows the rear brake light switch fed via a brown wire. Having studied a few of his generally really good wiring diagrams he sometimes confuses the letter B = Blu (blue) for brown which is marrone in Italian and shown as M on the factory wiring diagrams.

Don the indicators usually only work with the ignition on, the hazard switch is generally wired to the battery via fuse F5 or F6

Most older bikes, the indicators work with the ignition off, not sure about the newer ones. Certainly on a Mark 2 LeMans they will.

I don’t see how one brake light switch can work with the ignition off and the other with it on. It is a single wire down to the bulb with 2 switches feeding power into it. It would cause all sorts of problems back feeding power to the wrong places if it was half and half.

Don, I have looked at the Mk II wiring diagram (factory issue) you are correct the indicators are fed from fuse F5 which is permanently on, fuse F6 supplies the clock which again is permanently on. I eat a big slice of humble pie whilst writing, sorry.

As for the brake light switches, it would appear that when the fuse box was changed on the OP’s bike the supply to the rear brake light switch appears to be taken from the wrong fuse.

No probs Chris

On a similar vein, I have used a spare way from one of the lower (permanantly on) fuses to feed the starter relay. A neat and simple job.