Okay, I have now replaced the relay. I found out a few things in the exercise. First, I'm grateful I have small hands so that I could replace the relay without pulling it out! Second, I found out why it won't pull out. Evidently at one point the previous owner replaced the radio. I'm presuming they replaced it with one that was slightly longer and not quite as wide as the original. The length of the radio seems to be preventing the board coming out as it has trapped the rear (or front, depending on how you look at it!) relays behind the wiring. Also, I couldn't remove said radio because they kindly glued the darned thing in. Even if I had the "U-shaped" whatever is needed to unclip the radio (which the previous owners didn't use as the frame was broken and glued back together) it likely wouldn't have come out anyway with the amount of glue that was used. Thirdly, whilst all the other relays I could see were Volvo original (probably came with the car!) the flasher unit was not. When I finally managed to figure a way of taking it out, it was a generic part and it has severe scorching on one "pin".
So, I'm expecting this to be a part I will need to replace again at some point, presumably not for a while though
Thanks again... now... no ideas on why humidity in the cabin of the car makes the speedometer either go to 0 or 80?
Sam






