Would it be using battery charge even when the tomtom isnt plugged in? Id found an easy wiring behind the clock.
Since the clock feed is live, not ignition, it would depend on what is attached. If it is only some wiring with nothing to 'burn' any power then you have no problem. If there is anything like a transformer in that attachment, you could be using power even without the actual unit plugged in.
One thing to be aware of - sat. nav. units are highly desirable at the moment and top of the 'steal' list. If there is any, even slight, indication of the possibility of a unit in the car, you are a target. Now with our cars, if someone smashes a window, that is likely to be a bigger nuisance than the loss of the sat. nav. as it could take longer than an ordinary car to get a replacement fitted. It is even more annoying if there is nothing to steal so the window was broken for nothing! And worse, they may break the rear side window thinking they can then reach in and unlock the door, not knowing there is an internal glass. So they break that too. i have seen it done a few times... So make sure there really is no possibility that may make the car a target. (the obvious ones are sucker marks on the inside of the glass, stands, or aerials)
Roy