Some people are asking about the by=pass plug used for getting round gear problems and test boxes. From what I understand the original LT plugs and test boxes are only suitable for the AEC or Leyland engine version, they are not suitable for the refurbs with later gear control panels. the feed arrangements and polarities differ.

My bus number (if any): RML2532

Thank you to everyone for their useful advise and help. I now have the problem of the lost top gear sorted.
On closer inspection of the gearbox area, I noted a disconnected pipe on the nearside of the gearbox. Just a 5 minute job to reconnect the pipe and tighten the nut. Everything working correctly now!

My bus number (if any): RML2672

Makes a change to have a simple fix! Are they metal or plastic pipes from the EP block to the gearbox?

My bus number (if any): RML2532

Metal pipes

My bus number (if any): RML2672