Brian, Tom and John all provided comments and gave assurance my thinking was correct. It only took me a year to deliver the solution, some nice tick 8mm2 cable direct from the busbar to a fused switch next to the fridge.
I was hoping to use the old thin cable to pull through the new thick cable. This was not a success as I think Tony had correctly secured the cable bundles within the coving. So a delay was endured while I secured the correct cable 'fishing' device, basically a thin flexible drain type rod much thinner to be used to push/pull the thicker cable through.
This was undertaken last night with a decent degree of success getting the thick cable from the kitchen to the busbar in the engine room. After having made the connections beer was added to the fridge and the switch flicked......
..... a nice instant compressor tune sparked up and continued until after about 2 hours it cut out when the fridge got to temp. Over night the fridge stayed cold and did not play the fan song that we got before when the compressor would not start and we got the fan instead. A result and the fridge and other pump and lights use took 15% from the battery bank as advised by my Smartgauge.
So I will have a cold storage space .... until the temp turns the back cabin into a much larger fridge and the natural swap over coincides with the arrival of autumn and winter.
Its good to get the advice from fellow boaters so as and when we meet if I have cold beer you are due one.... of course I am talking larger, ales and red wine will be served at room temperature !
Onwards and upwards... now a back cabin stove for those winter cruise days - perfect !