You have to check each wire that goes to the switch that makes the light dim when you press it. The lights should not dim. Look for insulation that is missing, or cracked. You can also move the wires to different positions, and then try the offending switch. Another switch module would allow you to determine the condition of your current one. The only other part is the motor. Start with the wires, then the switch module.
You can take the connector off of the motor, and try the switch. If it continues to dim the lights, it is not the motor, unless moving the wires fixed the problem. That is why you check everything else first.
You can take the connector off of the motor, and try the switch. If it continues to dim the lights, it is not the motor, unless moving the wires fixed the problem. That is why you check everything else first.