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