Tail light not working

Hi, I have just failed my MOT on the tail light not working. Also, after trying to find a fault in the wiring, it appears I have done something as now the light doesn't come on when I pull the front brake. It does light with the back brake so I assume the bulb ( 2 filaments ) is ok.

The wires from the tail light to the plug have continuity. The fuses all work. However, I am unsure how to test further as my knowledge in wiring is very limited.

Any help is greatly appreciated. It's a 1981 KZ750 Ltd.

Shall we assume that you tested the fuses for continuity using a meter?

I don't know how different the 750 might be to other models, but there might be a brake light switch near/on the lower triple clamp below the headlight. If you were testing connections, etc. you may have dislodged the connector. The switch [in that location] will be attached to the brake hose.

One should not assume that a bulb is okay. It is possible the always-on filament in the taillight is indeed burned out, since it doesn't work and the brake light does. It may be difficult to see the fault in the filament but bulbs are cheap; you might as well replace it.

I assume you mean the brake light isn't working right. The tail light should come on & stay on when the ignition switch is ON.
The two operate independently from each other.

The front brake light switch should be at the Fr Br master cylinder. I would remove the switch & clean/check it.
To remove it you have to depress a tab located in a square hole on the underside of the master cylinder.
Depress the tab & pull out the switch.

Thanks for your thoughts.
There must be a loose connection as the brake light does work again.
I did check the fuses with a multimeter and have spares.
I have tried a spare bulb.

So now I think my main question is.... if I turn the ignition on and make my way along the connectors of the tail light wire and back probe each one will I find voltage?

For example, if I probed the brake light with the ignition on, the meter would have a voltage reading only when the brake is operated because it is on a switch? And therefore,, as the tail light is supposed to come on automatically when the ignition is on does that mean that wire always has a voltage reading when the ignition is on?

Does this make sense?

Yes, the tail light should always have power when the ignition switch is ON, and the brake light only has power when you apply the brakes. applying one or both brakes completes the circuit. make certain the tail/brake light bulb is good. it has 2 filaments., one for the tail light & one for the brake. The front brake light switch can get dirty.

FYI. The tail light has its own fuse, as does the headlight. The fuse box is embossed with TAIL 10A & HEAD 10A. The brake light circuit is on the main fuse.

ps: if you need a manual & wiring diagrams, search KZR for 750Turbo.com (manual) & mbsween (wiring diagrams)