Wiring: 4 pins transformed in 3 pins

Hello all,

Sorry for my english, I'm french.....

My current rear brake light is broken on my Electric Scooter (Aqiho Double Drive 2*1000w).

I'm trying to replace it but I have an issue with wiring.

Old light wiring:


New light wiring:


Well, the new one has only 3 pins with a common ground.

I tried this:


Unfortunately, brake light is turning on immediately after plugging the connector, even if the lights of the scooter are off and even if I don't brake.

Rear light is working well and turns on only if I turn on the lights of the scooter.

I measured voltage between +12v brake light pin and ground brake light pin from the controller, there is only a voltage when I brake, there is 0V if I don't brake.

I'm looking for a solution because I don't know how to solve it, I cannot add a second ground to this new light because there is no way to open it.

I'm thinking about this solution:


What is your opinion?

Thank you very much

The problem is that your bike is using the grounds to switch the lights, so if they have common grounds they both get switched if you use the brake ground, or neither gets switched if you use the tail ground.

The relay setup you show should fix that.

I tried a relay yesterday and it works now, this is a good fix.