Hello,
It sounds like that you are either missing the 12V supply to the brake light switch or there is a possible wiring fault.
First check fuse 9, 5A, at fuse box in passenger compartment. I have included a link below.
https://www.autogenius.info/volvo-xc90-mk1-first-generation-2006-fuse-box-diagram/
If this fuse is in order then check the connector at the brake light switch.
Pin 1, red wire , is supplied 12V from the fuse box to the switch. This can be done by either using a test light or a multimeter. How to use these please see below.
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
and
https://www.2carpros.com/articles/how-to-use-a-voltmeter
Using the below illustration of the wiring diagram you can also test the 2 wires from the brake light switch going back to the fuse box. The red wire supplies 12V from pin 11 at connector B to brake light switch pin 1 and the signal from the brake light switch comes from pin 5 at switch, yellow/red wire, to pin 34 at connector C. How to test a wire please see below.
https://www.2carpros.com/articles/how-to-check-wiring
Please let us know how you get along.
Cheers, Boris
Apr 7, 2021 at 5:08 AM
