[Richard Coutts-Smith]

Hi Robert, and a cheery hello to another Humber owner.
Unfortunately I can't help you with your question, my Corio made one ton trailer does have a lead on it, which looks original although I have updated the plug for a modern 7 pin for convenience.
There is as much knowledge on MLU about the Humber as can be found, so if you have not done so may I suggest trying the "Search" button.
Please feel free to share some pics and history of the truck.
Rich.