Ignition light on.

[eschaider]

You have three alternator design choices. If we use connecting wires at the alternator to identify each type, the three alternator types can be described as 1-wire, 2-wire, and 3-wire alternators.

1-WIRE ALTERNATORS

The 1-wire alternators are what is termed self-exciting. A self-exiting alternator is an alternator that has a specially modified voltage regulator that doesn't need a 12V ignition wire to activate it. The voltage regulator that controls the alternator output contains circuitry that uses the residual magnetism in the alternator's rotor fields to determine when to turn the alternator on and off. The regulator does this by sensing the alternator RPM; when it reaches a threshold RPM, the voltage regulator "turns on." Using this type of alternator, you would start the vehicle, rev the motor slightly, and the alternator would begin charging. Some Delco-based alternators, with a self-exciting voltage regulator, do not need you to rev the engine.


2-WIRE ALTERNATORS

Most standard alternators will use a two-wire setup. Two-wire alternators use the primary battery wire to the back of the alternator and also the ignition wire to activate the alternator. This setup allows the alternator to start charging as soon as the engine is running.


3-WIRE ALTERNATORS

Three wire alternators use a battery wire, ignition/warning light wire, and voltage sensing wire. Three wires in all. This is the design you want to use if you intend to support an ignition/warning light.

Voltage sensing is used when you want the alternator to read voltage at some other point than the battery, for example, when an extended length of cable is required to reach the battery. An excellent example of this would be a trunk-mounted battery.

You can use a self-exciting alternator with a trunk-mounted battery, I do. If you choose to use the self-exciting style alternator and it is based on almost anything other than a Delco CS series design, you will need to blip the throttle to get the alternator charging right after starting.

I use Denso internals with square wire and a hairpin winding in the small Ford 6G “T” mount case configured as a six-phase device because of both space requirements and the power budget forced on me by choosing a supercharged Modmotor. I set the engine start-up in my ECU to momentarily rev the engine to about 1500 rpm at start-up and then quickly return to normal idle. That immediate jump-up in engine speed at start-up turns on my alternator, so I don’t need to remember to blip the throttle.

While I have not tried the approach Morris has suggested, it logically sounds like it should work. When I did my electrical system, I didn’t think deeply enough to noodle out Morris’ solution. I do like it, and intuitively it does sound like it would work.

Disclaimer, I am not an electrician, and I don’t play one on TV ...