I assume Wales as in the British Isles. This means that all your important relays and computers are behind your battery. There is a plastic cover to be removed. In my 260e there is another small plastic cover over the OVP see fotos. See foto of FPR and OVP relay. You may have the newer type of OVP which has a red top and two fuses. Get the latest variant of the relay to suit your car. M.B. added variations to these relays over the lifetime of using them. This was always a problematic part