ok, I have completed the job.
I am not keen on the snap close piggy back connectors, so i removed the bullet connectors from the grips, stripped back about 1cm and the same on the sat nav lead, then twisted wires together with flux, a dob of solder and i am left with a 1cm tinned tail that fits perfectly into a red ballet connector.
I now have grips and sat nav on shared, switched aux outlet. All works great and makes a neat job. sorry, no pics as that is beyond my computer skills
Just ordered a Telferizer screen mount, so should be good to go for a test run early next week
To all of you for your input, everyone so helpful on here.