For What Its Worth

Internally Regulated Alternator

Wiring, Trouble shooting and LED dash light 

The 66 Chevy II came with an externally regulated alternator.   It had an external "regulator" box.   I have converted over to an internally, regulated alternator.   Same function, but the regulator is an IC circuit in the alternator.  Cleaner and more reliable IMHO.  If you ever had to adjust the old mechanical regulator you would understand.

This picture shows the wiring needed for an internally regulated alternator.

The Voltage sense wire usually connects to the Battery + or charge wire 12-18" from the alternator.  This gives the alternator feed back on the overall system voltage it is trying to maintain.

The green wire is from the keyed source, or alternator light.   This charges the alternator at startup.  Once the alternator is running and produces current the green wire will have + voltage on both ends causing the light to go out.

Trouble shooting

General wiring check

Disconnect the 2 control wires at the alternator. One is a power or energizing wire from the ignition, (#1) the other is a sense wire hooked up to the charging wire some distance from the alternator. (#2) The sense wire should be hot all the time since it connects to the battery + ciruit. The other has voltage when ignition on. Reversing these wires would cause the alternator to be "on" all the time.

The charging wire must be of the proper size and ties into the battery circuit.  Usually at a power bar that is part of the horn relay.  Make sure this is connected correctly and all connections are good.  IE proper, soldered ends or soldered connections.  No twisting wires together.

Alternator Checks

Most part stores can test an alternator.  But if you need to do some checks in the car, here are some tips.

When car is running use a voltmeter to check voltage at the battery.  Should be 13.5-14.5 volts with a good alternator.  When below 13, car is running off the battery only.

Alternator getting warm with the ignition off and battery draining

This may be bad diodes in the alternator.  The alternator appears to work fine, but will drain battery when parked.

Diodes keep the power flow "one direction". Out when charging, no flow back when off.  When they fail, power flows back through the alternator windings to ground.

To test diodes, with the key off disconnect the power/charging wire. Be careful, it is "hot" or going to the battery. Grounding it will cause a short!. Put an amp gauge between power wire and the alternator terminal it connects to. If there is a power draw, alternator is bad. Most likely bad diodes in the alternator. Replace the alternator.

Alternator light does not come on when Key ON, before starting car

Most likely cause, Alternator light in dash needs to be replaced.   Otherwise check the wire to the alternator that it is getting power at key on.  If not, find the wire fault.  If it is getting power and alternator not charging, replace the alternator.

Alternator light comes on when running

This usually means the alternator can not produce enough power and is failing. 

Alternator does not appear to charge the battery well

This could be a bad battery, weak alternator or underpowered system. 
The stock alternators only output 47 amps.  If you have high power headlights, the wipers on, the fan on, AC and a high power Radio, Fuel injection etc. You may not have enough alternator for all the upgrades. 

Alternator light conversion to an LED

The alternator light had 2 functions.   Warn you when the alternator could not make enough power to run itself and act as a resister to prevent feed back to the key when turning the car off.   If you have too much feed back to the key, the ignition could stay charged/running.

To replace the alternator light with an LED light you need to add a resister in parallel and solder in the LED on both ends of the resister.  The LED will not pass enough current to power the alternator startup otherwise.   Add a 1 amp diode to assure no flow back to the key power and you are good to go.  A 50 ohm 10 watt resister is what I used. Sort of a square blocky thing.  All available at Radio Shack.   Here is what it looks like in a wiring diagram.  Why does the light work?  When current flows to the alternator the resister drops voltage from one end to the other.  That causes the LED light to have a voltage difference and current flows through the LED and you get a light.  When the alternator works and creates its own current, the blue line in the diagram below goes from being a ground to a positive.  No voltage difference, no current flow and no light.  Works great.    Diodes only allow power flow one way, it is a double safety check to assure that no power goes back to the key circuit when turning off the car. 

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