1. Almost universally, aircraft master switches are set up with one side of the
switch grounded to the airframe and the other side of the switch to the "cold"
side of the master switch relay (or solenoid, if you prefer). The "hot" side
of the relay goes directly to the battery (+) lead. When you turn the master
switch on, it provides a ground for the relay and thus pulls in the relay
contacts providing you battery juice to the rest of the airplane.

2. The regs allow a small circuit breaker to also go directly to the battery
(+) terminal for such things as clocks, radio memory, and other things that need
juice full-time. As I vaguely recall without pulling out the regs, you can have
up to a 5 amp breaker, but it needs to be VERY near the battery box to minimize
the amount of unprotected wire running about the airframe. Most of us use a
small L-bracket mounted directly to the battery box and a VERY well insulated
short wire from the hot side of the master switch relay to the breaker.

3. Do yourself a favor. Get a small terminal strip (NEVER would I recommend
the Radio Shack #274-656 @ 2 for $1.69 for a certificated airplane) and mount
the terminal strip somewhere between the firewall and the instrument panel in an
easily accessable spot. Wire one lead of the terminal strip to airframe ground
and the other lead of the terminal strip to a wire going back to the
aforementioned keep-alive breaker on the battery box. Then wire the clock to
the terminal strip. Trust me, you will some day need to connect a radio or
other device to the keep-alive breaker and it is a hell of a lot easier to run
two wires to a terminal strip than another wire all the way back to the
tailfeathers battery.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com