Get yourself a VOM (Volt Ohm meter) at Sears or Rat shack or whatever
It will have a little booklet to explain how to measure things.
There's info online and at your local library too.
You need to measure resistance (OHMS) and DC Voltages (DV V)
in cars and sometimes current Milliamps ma -Amps A
Decent meters don't cost too much, $15-20 gets you an OK meter.

Once you get the meter and the Green book you can measure for power at the
various points to see where the circuit has failed. Maybe a broken wire or
bad ignition switch,fuse, relay, connector, whatever.
You will love your Green book, it makes troubleshooting much easier than
lousy generic schematics in Chiltons and Haynes, plus has important
parts location details.

Using a VOM is an essential auto electrical troubleshooting tool.
Parts substitution and listening for relay clicks, etc. leaves a lot
to be desired.

Bill