Disconnect plug again, and replace F11 in engine bay fusebox. I suggest the use of a small 8mm socket when removing two fuebox cover retaining nuts. Take care not to drop the nuts as you remove them.
The device that you reconnected is the oil vapour heater. They are prone to going short circuit, and blowing the "Secondary Services" fuse F11, which supplies several other items including the speedometer. The heater is part of the oil vapour recovery system, and is intended to stop watar vapour in the blow by gases forming ice crystals. Generally in the UK climate, the heater is not usually necessary so OK to run without it, However Scotland is a large area, and if you live in one of the colder parts you may wish to replace the heater. For replacements Coastal Motorhomes are frequently recommended when trying to obtain spares for older vehicles. My first recourse is usually Ebay.