Here are the major components you would need for this "project".
Vehicle Power Adapter for Nuvi 255W (Amazon search results).
"Bare wire" Cigarette Lighter Socket Plug Connector Adapter (Amazon listing)
OR something similar
That would be wired to the trickle cable with a mating connector OR perhaps wired to the battery directly, and would need to be mounted somewhere that is protected from any weather (mostly moisture).
As mentioned earlier, this may NOT be "pretty", but would get the job done.
Also, as I mentioned in my FIRST response, there are IMPORTANT considerations when trying to use a Nuvi in a "motorcycle" environment.
The Nuvi line are not really designed for exposure to the element - like the Zumo line of devices - which are designed specifically to be used on a motorcycle.
I suspect you are on a tight budget, but would recommend at least looking at the motorcycle specific devices, to see what they cost and the features they provide.
Search results for Garmin motorcycle GPS (Amazon search) - look specifically at the "Zumo" models
Please let me know what you find and if any of these solutions will work for you, or if you would like to discuss this further.
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