I have Honda heated grips on my motorcycle. The heating function works, but the LED does not light up when the heating is turned on. I have conducted some measurements myself and connected the controller to a lab power supply, but I cannot simulate the setup. Also, I cannot measure/find some points on the PCB. The gray wire is the power supply for the control. The green wire is ground, and the blue wire controls the LED. The LED has been tested with the lab power supply and it works. When I measure the voltage from the controller to the LED after pressing the button, it is 0.4 volts. It should be 5 volts. Can someone give me some help?

 

Can you not just put the led+series resistor across the heater, ?

 

I tried that but unfortunately it didn't work. In the meantime, I made a new discovery. On the base and collector of transistor Q3 (third photo top left), there is 12.3 volts, and when I press the button, the voltage drops to 11.2 volts, but the emitter remains at 0.03 volts. When I bridge the contact points, the light comes on. Now I think the transistor is broken, and by replacing it, the problem should be solved. But then I have one more question: which type of transistor do I need? The label on the transistor itself reads: F12 (30), but which type is most suitable?

 

So it's a PnP type, you can test it with a multimeter on Diode function, .