A wiring diagram is on my to-do list. I will have to take drawing lessons first. I have twin electric radiator fans, my voltage dropped a lot when I turned them on so I installed the Powermaster 3 wire alternator. It helped a bit but the voltage was still low so I checked it everywhere and discovered the voltage drops. The voltage regulator, internal or external, has a sensing wire. That wire inputs the circuit voltage, if the voltage is below 14.2 or so the regulator ups the alternator output, if the voltage is above the set voltage the regulator lowers the alternator output. Trouble is the sensing wire is connected to the soldered buss which is close to the alternator output and in a location that does not suffer from voltage drop. It keeps the battery charged but does little to detect voltage in the trunk. If I had connected the sensing wire to the ignition switch it would have sensed the lower voltage in the dash area and raised the alternator output. I already had the new alternator installed when I discovered the causes of the low voltage in almost every circuit in the car. When I pulled the engine to repair the rear seal for what seemed the umpteen time I removed every wire under the hood, save the ones attached to the windshield wiper, and made my own harness. I used heavy gauge wire and crimped, soldered then heat shrink wrapped every splice and connection. I installed a terminal block on the firewall with # 8 wire from the alternator and that is now my main buss supplying power to the dash area, the ignition relay, and the battery. It's also a convenient place to attach any accessories I may want to install. I ran a #8 wire to a second terminal block attached to the rad support and this is the buss for the fans, horn and headlight relays. Originally the headlight circuit went from the alternator, through the firewall junction, under the dash, to the light switch, to the dimmer switch, back out through the firewall junction, and to the headlights. Now juice goes from the terminal block to the relay and then the lights. The difference in headlight brightness is amazing. Obviously my car is not stock but most people who look under the hood do not notice the changes. Sorry for the long winded reply. You can wire in a relay by supplying battery voltage for the main power input and the stock distributor wire for the control [switch off and on]. It would be a good idea to put a fusible link or 10 amp breaker between the battery and the relay. A typical Bosch style relay will have the power from the battery going to the input terminal #30, the ignition wire to the switching terminal [off/on] #86, output # 87 terminal to the distributor, and # 85 terminal to ground. I ran the ground wire from the relay to the mounting screw but it may be a better idea to run it to a ground on the engine block. An HEI will put out more if it has a full 12 volts even better with 14+ alternator output volts. I you are getting good voltage to your distributor you don't really need a relay, but putting in a relay and fusible link or breaker sure won't hurt.
