Update.
Last night I installed the
hand guards.
(Yes, I know they are target sold for another brand of motorcycle.)
The wiring is inside of the head lamp.
I found a usable wiring diagram at the URL:
https://www.scribd.com/document/696345337/Bonneville-T100-Wiring-Diagram
Do a quick screen or windows capture to get an economical instance.
The running light is the smaller light bulb at the bottom of the head lamp. There is a small clamped down connector near the bottom at the inside of the head lamp cavity. Loosen the retaining screw and gently remove the connector. There is a white centre plastic hold pin in the source side of the connector. Use a small slotted screw driver to push it out of the back, wire side, of the connector. Have about half to centimetre of lead soldered on your hand guard wires. Gentle massage out the blue rubber grommet out of the running light source connector. You'll slide your ground and hot running light hand guard lines in this grommet. Gentle pry some space, small, on the wire in the connector. Push your ground line in against the black ground line in the connector. Put your hand guard running light source wires in the yellow/green running light source wire.
Test the new lighting. If all good, put the grommet and centre hold pin back together. Re-clamp the connector in the head lamp housing.
For the turn signal function of the hand guards, I used wire piggy back clamps to clip onto the appropriate source turn signal wire in the head lamp cavity. Easy to trace each turn signal wire.
The final aspect of the installation, is I did not permanently solder any of the new wiring in. It can be reasonably removed to return the T100 to its original styling. Wife told me they look to masculine.
As I am in the GTA area of Canada and to extend the riding season, the Triumph heated grips are nice, but not enough. The palms stay warm while the wind does eventually get to the knuckles through the gloves.
Here are some picture of the new hand guards.