Originally Posted by ggemelos
I am in the process of installing Hot Grips heated grips on my bike. I am wiring it to a relay triggered by the license plate light. The resistance of each grip is about 10.5Ohm. They are wired in parallel which means they will nominally each pull about 1.15A, 2.3A total. That is not a huge amount, but enough that I would not want to tied in to an existing circuit.
A rule of thumb in safety and electrical wiring. Half the Load or double the guage
. Another words put only 1/2 the max load on the guage wire you have or use a guage wire that is double the max load you will put on that circuit(see link to chart) When you tie into an existing circuit compute your max load(total=existing load + what your adding) then as long as the amperage is 1/2 or less max load for the guage wire it is on your safe. If not use a separate circuit or replace the existing circuit with bigger guage wire. Here is a good chart to follow in figuring out what load a particular circuit can handle: http://www.powerstream.com/Wire_Size.htm
ps. the taillight circuit is a 10amp line usually 16 or 18 guage wire so good to go with other loads noted in post #33602