[Roadsters] recommendations for a switched power source

[Tim]

I need to hook up an O2 sensor to a switched power source on my
Roadster. Since electrickery is a scary monster I am seeking advice
please.

The red wire is not very long and is most likely meant to be run to the
main ignition switch. Regardless of where I run it, it is not long
enough to reach to where I want to (temporarily) put the gauge (I will
not be using the gauge full time once my Webers are dialed it). Since I
will most likely need to lengthen the red wire, what are my options for
a switched power source under the hood? Is there a bbestb place to hook
up the red wire for the gauge?
Thoughts please folks.

Thanks!
tim