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 Adding an Alternator to a Big Healey - Alternator Wiring Connections 

(adapted from an article that I don't remember where I got it from!)

FINE PRINT: The information presented here is based upon First Amendment rights to say whatever silly thing one wants to. Anything that you might do, or any actions that might result from using this information is your own blooming fault. There is no way that this information is guaranteed to be 100% correct anyhow.

All internally regulated alternators have the same basic electrical connections. By comparing the descriptions below, it will be easy to change the instructions to suit the alternator you have chosen. If there is any doubt, take this write-up, along with the instructions for your particular car, to an alternator repair shop, and ask the counter man to identify the connections for you. Most places will be glad to oblige you, for a minimal fee, if any. Alternators typically have four external connections to the automobile's electrical system:

1.Ground. This is usually through the case, but some units require a separate connection, usually for the solid state regulator inside the case. If your unit requires a separate ground, run a short wire from the alternator to a convenient point on the engine block, or the chassis. If the connection is required for ground wire as you are using for the output, at least 10 Ga., preferably 8 Ga. 

2.Output. This connection carries the charging current from the alternator to the battery, and corresponds to the screw terminal on the back of the GM unit.  It connects directly to the battery, usually at the battery connection on the starter solenoid, or to the ammeter, if you car has one. This wire will be either Brown, or Brown with a colored stripe, in a Triumph.

3.Sensing. This wire connects to the battery, either directly, or via some connection in the main battery supply circuit. Typically, it connects to the battery side of the fuse block. Its purpose is to monitor the system voltage, and increases or decreases the charging rate, depending on the system load and/or battery condition. This is a smaller wire than used for the output, and is usually Brown or Brown with a colored stripe. This connections corresponds to terminal 2 on the GM unit. In some cases, this wire is self-contained within the alternator, and there will not be a connection for this function. If so, just omit, or insulate and tie off, the equivalent wire in the GM instructions.

4.Indicator. This lead receives voltage from the ignition switch, through the charge warning lamp, when the key is turned on, but the engine is not running. This serves two purposes - it gives a visual warning that the alternator is not charging, and provides the initial current to get the unit to charge until it can provide it's own charging current. This wire is almost always Brown/Yellow in a Triumph, and corresponds to terminal 1 on the GM unit. 

One-Wire Alternators 

Quite popular among the Street Rod set, the one-wire units are not really suited for our cars. The only advantage is the simplicity of connecting only one wire. This advantage is lost in a Triumph, because of the changes required to the existing wiring to allow the use of a one-wire unit. All the wires required for a three wire unit are in place, and would have to be disabled otherwise. There are two distinct disadvantages to the one-wire: They are more expensive, and the warning lamp function is not operable with them.

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, thatís 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 youíre 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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