10SI Alternator Wiring

 The 10SI has three terminals (including those with a 1 wire regulator).

The large "BATT" terminal that gets connected to your battery positive. (Or Terminal Post if your vehicle is so equipped). 

And a dual terminal connector. (Repair pig-tails for this connector available at any autoparts store. Or, salvage with alternator if pulling the alternator from a vehicle).

The #1 or "R" or Relay Terminal. (Marked with a "1" and "R" on case)  This terminal provides a pulsing DC signal that varies with engine rpm. The voltage is half system voltage as measured with a voltmeter.  This terminal is used to connect to the dash warning light, or used as a tachometer connection (such as diesel engines that have no ignition system to get a pulse from). 

For the warning light, a lamp is wired in series with a switched voltage source. During normal operation the lamp stays off. If the regulator is damaged, the #1 terminal provides ground, and the warning lamp will light.  This terminal is also active on 1 wire regulator equipped 10SI alternators.

The #2 or "F" or Field or Sense Terminal. (Marked with a 2 and "F" on case)  This terminal is used to excite the 10SI into operation. (3-wire 10SI) It is connected to the battery positive.  For simplicity you can connect the #2 connector pigtail directly to the "batt" terminal on the alternator.  The terminal is present on 1 wire regulators. Used only for those that require the stock connector to fit snugly. 

If you are converting from a 3wire 10SI to a 1 wire regulator you can hook up all your stock connectors, and run it as is. However, that’s wasted money unless you plan on cleaning out some wiring under your hood. 

If the 1 wire is for cleaning out wires, you only need to retain the "BAT" wire. The #1 & #2 terminal wires can be eliminated. Don't be surprised to find that the Field (#2) wire only goes a short way into the harness and spliced into the "BAT" wire. The 1 wire regulator comes with a dust plug for the #1 & #2 terminals. 

Use a voltage gauge to monitor your charging system. It will definitely give you signs of impending problems. (Bad regulator, failing battery, etc.) 

If you’re looking for a high output unit, keep an eye out for your everyday rebuilt (re-stamped 63amp). In my case, my rebuilt puts out 80amps at high rpm. More than enough for most anyone needs. 

High output aside, don't expect your alternator to do anything for you at idle speeds. Alternator output increases with rpm, even a 100amp unit won't put out much more than a 63amp unit at 1000rpm.

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