Focus Zetec Climate 1.6 2005 Mark 3 Parking Sensors Not Working

Hi there, new to the forum hope I haven't put this post in the wrong area. I bought the above car last night. I knew they weren't working when I bought it but as they aren't standard on this model and I figured that fixing them can't cost more than installing them I wasn't worried and would try sort them myself. I have seen a lot of topics where both the reverse lights and the sensors are faulty, this is not the case with mine. the reverse lights work fine it is just the sensors and there is no sound at all. I know normally the sensor fuse is part of a relay with the reverse lights so one couldn't work while the other is broke right? As the sensors where an extra is it possible that they have an independent fuse instead of running off the relay? Please don't get too high tech I'm not a mechanic nor do I fix cars on the side. At best I can do the most basic maintenance and check fuses! :)