Sidelights and tail lights run from the #9 10A fuse (in the engine compartment fusebox FB1).
A red/black feeds the tail light relay (in the under dash fusebox FB2), continued on with another red/black to each of the sidelights, tail lights and number plate lights, plus another red/black provides backlightling to the interior switches and audio unit.
The back of the headlight units and main lighting loom may be reached by partially removing the wheel arch liners, but you might be able to pick up one of the other lighting wires on route between the fusebox and each light.
The panel under the driver's knee shelf is easily removable - one twist lock and then it can be pulled down from a couple of friction fittings.
One word of caution - the red/black colour wire may also be used for other components, and the DRL's should be run from a low rated fuse either using a spare slot or a fusetap, not directly connected to the battery.
http://www.hondafitjazz.com/manual.html > wiring diagram > index > exterior lighting (4)
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TG