MSD 8975 Installation

MSD Digital Retard Control

PN 8975

IMPORTANT: Read the Instructions before attempting installation.

Parts Included:

1 - Retard Control, PN 8975
4 - Mounting Screws

Note: The Digital Retard Control must be used with an MSD 6, 7, 8 or 10 Series Ignition Control. Do not use

solid core spark plug wires.

OPERATION

The MSD Digital Retard Control uses a high speed RISC microcontroller to control the timing output
signal. This controller can make extremely quick compensations to the output signals while keeping timing
accuracy to within 1°. The circuits are thoroughly debounced and isolated to create protection against
Electro Magnetic Interference (EMI).

There are four stages of retard that can be activated independently or together for a total sum of retards.
Each stage is adjustable from 0° - 9°. The maximum amount of retard is 20° even if the total of the stages
is more. There is also an optional start retard circuit that can be programmed for 5°, 10°, 15° or 20°.

MOUNTING

The Digital Retard Control can be mounted under the hood, but should be away from direct engine heat
sources. Make sure all of the wiring reaches their connections. Use the unit as a template to mark the
location of the mounting holes. Remove the unit and drill the holes using an 1/8” drill bit. Use the supplied
screws to mount the Control.

WIRING

RED

BLACK

YELLOW

There are two input trigger circuits. The wires will never be connected at the same time.

WHITE

GREEN/VIOLET

2-Pin Connector

When more than one channel is activated at a time, the retard amounts are cumulative (Example:
4° on the first stage, 3° on the second and 3° on the third, equal a total of 10°). The total amount
of retard that can occur is 20° even if it is programmed for more.

BROWN

ORANGE

GRAY

DARK BLUE

Note: If you are not using all of the retards, set the rotary dial to 0° or ground the inactive

circuit's activation wire(s).

This is the On/Off wire. Connects to switched 12 volts.

Connects to Ground.

Trigger output. Connects to the MSD Ignition's White Wire.

TRIGGER INPUTS

Connects to points or the amplifier trigger wire.

Connects to the magnetic pickup of the distributor or crank trigger. Green is
negative, Violet is positive.

RETARD CONTROL WIRES

Retard 1, Activated when removed from ground.

Retard 2, Activated when removed from ground.

Retard 3, Activated when removed from ground.

Retard 4, Activated when removed from ground.

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2 INSTALLATION INSTRUCTIONS

PROGRAMMING

CYLINDER SELECT

The Digital Retard is programmed at the
factory for operation on 8-cylinder engines.
If installing the Control on a different style
engine, the number of cylinders will need
to be selected on the Cylinder Select Dial
(Figure 1).

Figure 1 Programming the Cylinder Select.

MAGNETIC COMPENSATION CIRCUIT

This circuit provides a timing compensation for different style magnetic pickups. Magnetic pickups can
have varying thresholds and being able to program the style pickup you use provides a more accurate
and stable timing signal. This adjustment is more important for engines using crank triggers or locked-out
distributors. If you are using the White wire to trigger the MSD, no adjustment is necessary.

Note: It is recommended to check your Total

timing to ensure the best setting for
your application.

START RETARD

When programmed, the Start Retard will
retard the timing during cranking to ease
starting. The amount is adjustable with the
rotary dial on the side of the unit (Figure

2). The retard will be activated only during
cranking and will remain activated until
the engine reaches 800 rpm where it then
returns to the set mechanical timing. If the
engine speed drops below 500 rpm, the Start
Retard will activate again.

Figure 2 Programming the Pickup

Compensation and Start Retard.

RETARD RATE

There are four different stages of retard that are activated by individual wires. When the corresponding
wire is removed from ground that retard amount is activated. Each retard selector switch is adjustable
from 0° to 9° (Figure 3).

When more than one channel is activated at
a time, the retard amounts are cumulative
(Example: 4° on the first stage, 3° on the
second and 3° on the third equal a total of
10°). The total amount of retard that can
occur is 20° even if it is programmed for
more.

Note: If you are not using all of the retards,

set the rotary dial to 0° or ground the
inactive circuit's activation wire(s).

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Figure 3 Retard Stages and Activation Wires.

INSTALLATION INSTRUCTIONS 3

Figure 4 Wiring an MSD 6 Series Ignition with Points/Amplifier.

Figure 5 Wiring an MSD 6 Series Ignition with a Mag Pickup.

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