You're

!
I'm a bit sceptical about the Dealer ordering a "wiring harness".
The Trophy has a dedicated "clean" Power suppply for Sat Nav's,
which is a moulded Socket buried away and taped to the main harness
behind and below the left mirror pod.
I suspect the "Wiring Harness" your Dealer is ordering is this :
Triumph GPS Accessory Cable which has a plug on one end
to connect to the Trophy Sat Nav Power socket,
and bare wires on the other end to connect a
12V Sat Nav device to.
You won't be able to connect that directly to your Nuvi,
so ask your Dealer NOT to install the Bracket yet,
until you have sorted out the correct wiring,
otherwise you WILL have to take it all apart again !
Garmin state that "in the box" with this Model of Nuvi,
is a USB cable and a 12V "Cigar lighter" type of power cable,
either of which can be used to plug into a Mini or Micro USB socket
on the back of the Nuvi device.
( Unfortunately there is no information on the Garmin site
as to whether it is a Mini or Micro USB socket ).
You would therefore need an adaptor cable to connect to the bare 12V wires
of the Triumph GPS Power accessory cable, with a Micro or Mini USB Plug on the other end.
Something like this :
12V to 5V Hard Wire Adapter Cable Mini USB Micro USB - on eBay UKI'd also recommend ( as per the Sat Nav bracket installation Topic
referred to in my previous Post ) that you insert an In-Line Fuse holder
between the triumph GPS accessory cable "+" ( red ) wire,
and the adaptor cable that feeds the Sat Nav device,
and route the wiring so that the Fuse Holder sits behind the left mirror
where it can be easily accessed if the fuse should ever blow
Cheers

