Join Date: Aug 2009
Location: Washington, the state
You simple questions don't have simple answers.
1--A "hot wire" has positive 12 volts on it. It can have that voltage either because it comes from the battery positive post, or because some device switched it on under certain circumstances. Whether or not it can be tapped to run something else depends on when it is switched on and how much power the new gizmo will take from it. It too much power is taken the wire gets too hot and melt$.
2--It's too bad we can't get away from the word "ground." Nothing on a motorcycle is grounded to earth the way house wiring is grounded. Very little on our motorcycles is bonded to the frame (called ground) due to the combination steel & aluminum frame. What we call "ground" is actually connected to the battery negative post. Again, sometimes we can connect to another negative wire, and sometimes we need to run a new negative wire to the battery to handle big electrical loads (horn, lights, electric heated clothing, etc.).
3--Keep in mind that "the tail light" is actually two bulbs with two filaments each (three wires for each bulb--hot tail, hot stop, shared negative) in close proximity to two turn signal lights and the license plate light. All have their wiring.
None of this directly answers your questions, but I hope that with all the answers we can help increase your understanding of vehicle electrics.
"Older people who are reasonable, good-tempered, and gracious will bear aging well. Those who are mean-spirited and irritable will be unhappy at every period of their lives.
"Let each of use properly whatever strengths he has and strive to use them well. If he does this, he will never find himself lacking."
Marcus Tullius Cicero