Due to the number of different alternator brands and configurations, the following procedure has been generalized to cover the most common configurations. Consult the alternator manufacturer for any information that is not covered in this procedure.
Typical DelcoTM Alternator Wiring System
Indicator (I) Terminal
The main function of the indicator (I) terminal is to indicate if the alternator is working correctly. Typically, an indicator light is wired to this terminal. If the alternator is not charging properly, the light turns on. Another function of the indicator (I) terminal is that it can be used to supply up to 1 ampere of output at system voltage.
Lamp (L) Terminal
Similar to the I terminal, the L terminal is used to indicate if the alternator is working correctly. The difference between the L terminal and the I terminal is that the L terminal is a current sink only and can not be used to reduce turn on speed.
Relay (R) Terminal
The function of the relay (R) terminal varies. It can supply up to 4 amperes of output at one-half nominal alternator
voltage to power items such as a tachometer or an hour meter.
One-Wire System
This is the simplest of the wiring systems because the only wires connected to the alternator are at the battery (BAT)
and ground terminals. (See the illustrations below.) Connecting to the R terminal, L terminal, and I terminal is optional.
Three-Wire System
This system requires more wiring because it has a battery (BAT) terminal, R terminal, two blade terminals identified
as number 1 and number 2, and a ground terminal. Typically, in the three-wire system, the number 1 blade terminal
serves as the I terminal. (See the illustrations below.) The advantage of the three-wire system is that it provides the
same features as the one-wire system, plus remote sense. By connecting the number 2 blade terminal to the battery’s
positive ( +) terminal, the voltage is both sensed and regulated at the battery, instead of at the alternator. This
eliminates the potential for voltage losses in the wiring from the alternator to the battery.
