The #2 spade on the alternators regulator connection may be either powered full time, or may be wired to be on/off with ignition - either will work. *For repair harness including diode see part number 9840-4033* Depending on switch circuitry there may also be a diode before the #1 spade to prevent the current when charging from back feeding the ignition switch and not allowing unit shut down. This connection acts as a ground allowing the no charge indicator light to work, until the alternator starts charging - the alternator will then push 12v+ back up towards the indicator light cancelling out the circuit and shutting the light off. With key on power is then transferred through the no charge indicator light to the #1 spade on the alternator regulator connection. The ignition switch is most commonly powered from the starter battery stud, but source may vary depending on application. *This diagram shows the simple wiring diagram for negative ground Delco SI series alternators.* If you are looking for the no charge indicator light on the dash to function as well, this should help determine which connection to use.
While this series of unit often runs as a self exciting one wire, agricultural applications also used 3 wire connections to the alternator. We are commonly asked how to wire the Delco SI series alternators upon maintenance or upgrading from an older generator.
