The car has a negative ground system right? If you search relays they are many diagrams and they are used for different things like headlamps, horns, electric fans etc. it is very simple. They can be wired into an existing system.
An example:
Starter, I positive wire from the battery (+) and one wire from the ignition switch to the solenoid.
Ignition coil, 1 wire from the ignition switch or fuse box to the + terminal of the ignition coil and the (-) marked terminal to the contact point and condenser inside the distributor.
Alternator, 1 wire goes to the battery from the alternator this is the larger gauge terminal usually round. The smaller contacts are for a wire that also goes to the ignition and another goes to the charging light.
I hope some of these help. Good Luck having a tester would be of great help.