removed the upper dash ( radio surround)and manged to get my hand behind it and pull out plug, connceted two wires and put the switch on.
drove with it and flicked teh switch and bingo, Nav lit up and allowed me to input address etc, once complete flicked the switch again and normal mode.
At this point no challenges graphics everything work great.
This will save time rather than pulling off the highway to change directions.
thanks everyone.
05 Hummer