7.1 Basic / Load Sections 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
• S - Sense. Used in some applications to allow the alternator to monitor the voltage at a different point from
its own output terminal. Not used with MS3Pro.
There are several ways you can run these alternators.
Simple installation This is the approach used on the MS3Pro drop on harness. Simply connect one side of
a suitable alternator warning light to a switched 12 volt source, and the other side of the warning light to the “L”
terminal. We recommend putting a resistor, at least a 1K, 1/4 watt unit, in parallel with the warning lamp so the
alternator will still function if the warning light fails.
On/off control This allows the ECU to shut down the alternator during cranking and for a few seconds
afterward. This can help with smoother startup, particularly if you are using one of these alternators on a small
four cylinder engine or a wildly cammed engine that has difficulty idling. In this case, you would connect the “L”
terminal to a 1K resistor, with the other end of the resistor wired to a switched 12 volt source. Then you also
connect the “L” terminal to an unused high current or PWM output, allowing the MS3Pro to ground this pin and
shut off the alternator.
Settings:
• Control mode: On/Off
• Control output: Use any available high current or PWM output.
• Output polarity: Inverted
On/off control with load monitoring Not all CS alternators support this feature. To find out which sort you
have, unplug the four pin connector and measure the resistance between the “L” and “I/F” pins on the alternator
side. If you measure approximately 400 ohms, the “I/F” pin is an ignition output and does not support load mon-
itoring. If you measure 1000 ohms or more between these pins, the “I/F” pin is a field output pin and provides a
pulsed output which the MS3Pro can use to monitor the alternator load.
The wiring is the same as for on/off control, except that you will wire the “I/F” pin directly to a digital frequency
input pin.
Settings:
• Control mode: On/Off
• Control output: Use any available high current or PWM output.
• Output polarity: Inverted
• Load monitor: Use any digital frequency input pin.
• Capture polarity: Inverted
7.1.8.5 Chevrolet 2 wire alternators These alternators began to appear on General Motors products in the
mid 2000s. These are sometimes called RVC, for remote voltage control. These alternators have true ECU control
with a 128Hz 0-5V PWM signal to the "L" terminal. When the alternator is off or in fault conditions, the alternator
pulls "L" to ground through a ~390R resistor.
The pins are as follows:
• L - Lamp. Used as an input to control alternator voltage.
• F - Field. This is a variable duty cycle output to indicate alternator load.
The signal uses a variable duty cycle to command a voltage to the internal regulator circuit.
Commanded voltage Duty cycle
11.0 V 10%
11.8 V 26%
12.8 V 42%
13.7 V 58%
14.6 V 74%
15.5 V 90%
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 137
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