Which relay for brake lights?
 

This is what my fuse board looks like. I need to replace the brake light relay but struggling to find the appropriate diagram to locate which one it is. Really hope it's one of the accessible ones! If not I guess you have to free up the boot liner enough to remove the fuse board?

How do you know you need to replace a relay if you don't even know where it is?

Tail lights out (lowers only). Not bulbs so assume relay.

There has to be better way to access than sticking a crow bar in there!

That approach will waste you a lot of time and effort and probably cost you money replacing the wrong part. Do a proper diagnosis first, then swap parts.

There is! Remove the side panel (4 screws)

Skiffy, You are on the right track. I had the same problem. Both lower brake lights on mine were out, but the high mount brake light came on. The brake relay was faulty. One of the contact on the relay armature broke loose. Unfortunately, you'll have to remove the rear quarter panel to gain access to the brake relay. Volvo could have easily move the fuse panel back a few inches for proper access. I don't remember which position the brake relay was in. I used one of the unused neighbouring relay as a temporary substitute until I could get a replacement.

Success!

I had emailed volvo for a quote to replace the relay. They said it would be about £30 but very unlikely to the be the relay as ththey would all be put and I'd be better off paying £70 for a scan. I called bull**** on that saying the lower ones have their own relay.

So I paid £4 for a generic (correct) relay off ebay http://tinyurl.com/ya58zjcb

Then after a while of fiddling I worked out a way of replacing it without a) pulling the boot trim off or b) using a crow bar. If you pull out the relay at the top by the clip that holds the fuse board in, and pull the trim panel away a little bit, you can get just enough rotation on the fuse board to dislodge it from its mount. Then you can wiggle it aft into the opening. Then you can actually grab hold of the relays. Pulled a couple out until I saw number 15, stuck the new one in and bingo, working brake lights, for £4.

Good result!