Final answer:
The function of the door relay (30-100) in cars is to control the power supply to the electrical systems related to the doors.
Step-by-step explanation:
The function of the door relay (30-100) in cars is to control the power supply to the electrical systems related to the doors. It is responsible for ensuring that the doors can be locked and unlocked, that the interior lights turn on and off when the doors open and close, and that the power windows function properly.
The door relay acts as a switch that allows or interrupts the flow of electricity to these systems. When a door is opened or closed, a signal is sent to the relay, which then controls the corresponding electrical components based on the input it receives.