Technical information

AUTOTRONIC CONTROLS CORPORATION • 1490 HENRY BRENNAN, EL PASO, TEXAS 79936 • [phone] • FAX [phone]
www.msdignition.com email: [e-mail]
79
SWITCH OR
MICRO SWITCH
PN 8820
TO GROUND
TO 12V
RED
BLACK
TO MODULE SOCKET
TO LINE LOCK
OR TRANS-BRAKE
SOLENOID
MODULE SELECTOR
STEP
MODULE 2 MODULE 1
PN 8739
AUTOTRONIC CONTROLS CORPORATION
1490 HENRY BRENNAN DR, EL PASO, TX 79936
TM
The MSD Two Step, PN 8739, Three Step, PN 8737, and Launch Control, PN 8735, Module Selectors allow you to
switch between two or three different rpm or retard modules. The different modules are activated when 12 volts
are applied to the corresponding wire. They must be used with an MSD component equipped with a rev control or
timing control module.
Wire F unctions
Two Pin Connector: Plugs into the module holder of the MSD component.
Black: Connects to engine ground.
Red: Activation wire, when 12 Volts are applied.
Blue: Activation wire (Three Step and Launch Control only), when 12 Volts are applied.
Two Step Operation
When there is 12 volts applied to the Red wire, Module 1 is activated.
When no voltage (grounded or open) is present on the Red wire, Module 2 is activated.
Three Step Operation
When there is no voltage present on the Red or Blue wires, Module 2 is engaged.
When there are 12 volts applied to the Red wire, Module 1 is activated.
Where there are 12 volts applied to the Blue wire, Module 3 is activated.
If the Red and Blue wire are activated at the same time, only Module 3 (Blue wire) will be activated. Module 3
overrides the other modules.
Note: Page 81 has information about the MSD Launch Control, PN 8735.
BASIC TWO STEP MODULE
SELECTOR INSTALLATION
When 12 volts are applied to the Red wire of the Two Step (button depressed), Module 1 will be engaged. When
the button is released, Module 2 will automatically engage.
TWO AND THREE STEP MODULE SELECTORS
Note: This is the module
socket in an RPM Switch, Rev
Limiter or Timing Computer.