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Hi another wiring question if I may. On my loom which is a new one there are 3 wires going to the rear light. Blue/black, black and yellow. On the light itself is an earth wire and then a red and a brown. I can't get both the brake light and the rear light to work correctly. The wiring diagram that came with the loom just shows yellow and blue black going to the switch. Any thoughts much appreciated.
Mike

Sorry yellow and blu/black going to the light not switch

Do you have a source of power available? I would start by testing the taillight to identify the brake light wire and the taillight wire. A 6-volt lantern battery would work, as would a 6-volt batter charger.

Clip the negative (black) lead of the battery or the battery charger to the earth ground wire on the taillight, then one at a time touch the red (positive) lead of the battery or battery charger to the red and brown taillight wires. The brake light will be brighter than the other light and if you are using a battery charger it will show a higher amperage draw.

With regards to your loom. black is usually earth ground. Does the bike run? I would put a voltmeter's black (negative) test lead on the black wire of the loom appearing at the taillight and then use the meter's red lead to measure voltage on the blue/black and yellow wires. Whether you set the meter to AC volts or DC volts depends on your bike's electrical system.

With the lights turned on one of the wires should show a voltage. When the lights are turned off the voltage should disappear. That would be the taillight wire. Then move the red test lead to the other wire. That wire should show a voltage only when you activate the brake pedal.

If all this goes well, you now know which wires of the loom are brake and taillight and which wires of the rear light are brake and running light and you can join them together. Also connect the ground wires together.

Jim

Thanks Jim followed your tip and all sorted now but there is a wire not used. Whether it is to accommodate a different rear light not sure, mine is CEV
Thanks again Mike

Is this unused wire at the taillight? What color is the unused wire's insulation?

Jim

Your stoplight should only have two wires to it and earthed to the frame at the light. The yellow and blue wires are correct. Where did you get your loom? And what model is it supposedly for?

Hi I got the loom from classic ducati for a widecase scrambler. The unused wire is black.
Thanks
Mike

Original looms used the frame for ground. Given the levels of vibration from a single, it's not a bad idea to rubber mount certain parts ands use a separate ground. I suspect the black wire is a ground wire. Just use a multimeter and see where it goes.