Brief explanation, the US (Domestic) have running lights in the indicators, this is achieved simply by using what we use as a stop tail dual filament lamp, 21/5w the higher wattage as the indicator, the lower as the running light, so their lamp holders have two pins & indicator wiring three leads, Indicator live, running light live & earth.
HDI (UK) only have the single pin light holder, so only two leads, Indicator live & earth.
So basically you have to feed the running light live (White lead in kit) through with the existing indicator wiring route to inside the bat wing, to be honest I suspect that will be the hardest part of the job!
Where to pick up a 'running light' feed as said you could use the P&A power connector, or tap in as Andy in Beds into connector 31, there are a few other options as well.
However, I would suggest one of the best places to take a running light feed live is off the lighting circuit from the connector that is not being used on the Street Glide, the Fender tip light.
The advantages of using this feed over the others are, this is the appropriate to the lighting circuit and the CanBus monitoring of this circuit has the spare capacity not to trip any fault codes due to extra load etc. (unlikely with LEDs) and will function in the accessory position.
No splicing required, you just need a AMP/TYCO connector & pins. (see below)
AMP/Tyco Multilock (70)
Fender Tip lamp connector [32](& P&A Power [299] same connector)
H-D part numbers
73152-96BK Socket housing 2-way x 1
73191-96 Socket (connector) x 2