Should be the brake vaccum switch. Side effects are mushy brakes. This should be the part. Heading to bed after this post, so just double check the part number or wait for someone to confirm with me. https://www.fcpeuro.com/products/volvo-booster-vacuum-switch-s60-v70-xc70-s80-genuine-volvo-31265825...

Yes, it is the vacuum switch for the power assisted brakes. When there is low vacuum in the manifold, the switch tells the vacuum pump to run to enable power assist for the brakes. It looks like you are missing the electrical connector from the top of the switch. You will probably need: a new or rep...