You could theoretically power the grips as well as the satnav off the spare connector behind the dash, but you'll be getting very close to the limits of the 10A supply available at that connector because it on a circuit which also supplies the sidelights, tail light, number plate lamp and indicators (as well as your satnav).

The failsafe option would be to use the spare connector's supply to trigger a relay and run the load for the grips direct from the battery via the relay. Trouble is there isn't much space up front to hide a relay other than behind the grey panels. The alternative is to do the same thing but trigger a relay off the tail light supply and stash it under the seat where there is more space.

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