Vehicle indicator illumination circuit and method for controlling vehicle indicator illumination circuit

A power supply route for a light source (3) includes a first route (R1) that closes when a microcomputer (2) is operated and a second route (R2) that opens when the microcomputer (2) is operated. When the microcomputer (2) stops operating, the power supply route of the light source (3) is automatically switched from the first route (R1) to the second route (R2). When the microcomputer (2) is operated and a position lamp switch is turned on, current is supplied to the light source (3) through the first route (R1). When the microcomputer (2) stops operating and the position lamp switch is turned on, current is supplied to the light source (3) through the second route (R2).