How does a lighting system in a car work?

Answer 1

The car battery prides the current. The negative terminal goes to the chassis, called ground. The positive terminal goes to a fuse box to protect the wiring harness from melting during a short condition, and then to a switch that turns the lights on and off. From the switch to the light bulb. For dome lights there are two switches, one on the door frame and one on the dome lights.

Lamps that draw a lot of current need heavy gauge wire to prevent the wire from getting warm and to reduce the loss in voltage due to wire resistance. In those cases, the heavy gauge wire goes to a relay near the lamp, so it can be kept short. The light switch on the dashboard energizes the relay, which doesn't need much current to turn on, thus can use smaller wire.

For turn signals, there is an additional switch that uses a bi-metal contact (flasher module). Bi-metal has two dissimilar metals laminated together. When current passes through the contact, it gets warm. The two metal expand with temperature at different rates so the contact starts bending. After a few hundred milliseconds, the contact bends open and current stops flowing. The contact cools and then reconnects the circuit. The cycle repeats and the lamps flash.

Since the current causes the contact to heat, the amount of current can affect the rate of bending. Often when trailer lights are connected, the lamps flash faster. In addition if a bulb burns out, the lamps may flash slower. improvements in the flashers, heavy duty flashers, and solid state flashers reduce the sensitivity to current flow.