when I push the yellow button both yellow and blue are activated

Hola heyhoy52 ¿cómo estás?, I'm from Colombia and I hope your okay, first of all happy new Solar Cycle.

Probably what's causing your issue is the connection between the cables and the PCB (the board), so I strongly recommend you to chek this, look at the picture please. If it's necessary cut the first 5 or 8 millimeters of the cable and solder to the PCB again.

First, check if the PCB board inside the neck has been worked on before. It sounds like someone tried to fix it previously and their soldering bridged between the two contact points. Check both ends of the wires for soldering that bridges two connections.