MSD 8680 Installation

Adjustable Timing Control

PN 8680

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IMPORTANT: Read the instructions before attempting installation.

Parts Included:

1 - Timing Control, PN 8680 1 - Control Knob
1 - 3/8" Bushing 1 - 2-Pin Weathertight Connector
4 - Self Tapping Screws

WARNING: During installation, disconnect the battery cables. When disconnecting the battery,

always remove the Negative cable first and install it last.

Note: The MSD PN 8680 Timing Control must be used with an MSD Ignition Control. It is recommended

to install the MSD Ignition first.

MOUNTING

The Timing Computer may be mounted in the engine compartment as long
as it is away from direct engine heat sources. Make sure all of the wires reach
their connections before mounting the unit. Use the Control as a template
and mark the mounting holes. Remove the unit and drill the mounting holes
using an 1/8" drill bit. Four self tapping screws are supplied to mount the unit.
Note: Before mounting the unit, install the supplied grommets and sleeves
as shown in Figure 1.

PROGRAMMING

The Timing Control is programmed for 8-cylinder. If installing the PN 8680 on
a 4 or 6-cylinder, the Control must be programmed.
Locate the Cylinder Select cover on the side of the
unit and remove the single Phillips screw (Figure 2).

CYLINDERS CUT LOOPS

Number of Cylinders: The Red loop and the Blue
loop are responsible for cylinder programming. The
chart in Figure 2 shows which loop(s) to cut.

8 NONE
6 RED
4 RED AND BLUE

Note: After cutting a loop, position the wire ends

away from each other so they cannot make
contact.

Figure 2 Selecting the Number of Cylinders.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

Figure 1 Installing the

Vibration Mounts.

2 INSTALLATION INSTRUCTIONS

WIRING

Figure 3 How to use the Supplied Wire Splice Device.

WIRE FUNCTIONS

Yellow This is the trigger output wire. It connects to the White wire of an MSD 6 Series Ignition or

“Points” terminal of a 7 Series Ignition.

Red This wire is responsible for turning the Timing Control on and off. It connects to switched

12 volt source. It can be spliced into the small red wire of the MSD.

Black This is the ground wire and must be connected to a good engine or chassis ground.

TRIGGER WIRES

Violet These wires connect to the magnetic pickup of the distributor or crank trigger. The
Green Violet is positive (+) and the Green wire is negative (-). When this connector is used

the White wire is not.
White This is the trigger input wire for breaker points or ignition amplifier. When this wire is used,

the magnetic pickup wires (violet and green) are not.

Control Knob

The Black and Gray wires with the 2-Pin Weathertight connector are the Control Knob wires. After the
Timing Control is mounted, the Harness should be routed to the unit. The Control Knob should be
mounted within easy reach of the driver. Before mounting the Control Knob, make sure the wiring harness
reaches the unit.
If the harness must be routed through the firewall, drill a 3/8" hole and use the supplied grommet to route
the wires through. Install the supplied 2-Pin Weathertight connector to the wires after all of the routing is
finished (Figure 4). The position of the wires in the connector is not important.

Figure 4 Installing the Weathertight Connector.

Operating the Control

After installation, it is recommended to check the timing. Before starting the vehicle, turn the Control Knob
to the full 15° mark. This is the stock timing setting. As the Knob is turned counterclockwise, the timing
retards. As detonation occurs, slowy retard the timing until the “pinging” noise is not audible. Adjust the
timing as driving conditions change.

Resetting the Timing

It is possible to set the Timing Control up to where you can retard and advance the timing 7.5° each.
To do this, position the Control Knob in the center (approximately 7.5°) then reset the timing to factory
specifications.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4

BLACK

BLACK

WHITE

WHITE

RED

RED

YELLOW

FROM IGNITION

KEY

INDICATES CONNECTION USING

WIRE SPLICE DEVICE

TO GROUND

ORANGE

MAG PICKUP

NOT USED

NOT USED

TIMING

CONTROL UNIT

TACH

OUTPUT

IGNITION

Multiple

Spark

Discharge

MSD

COIL

C+

C-

POINTS

OR AMPLIFIER

DISTRIBUTOR

ORIGINAL

COIL WIRE

-

ORIGINAL COIL+ WIRE

HEAVY RED

HEAVY BLACK

TO BATTERY+

TO BATTERY-

A

D

V

A

N

C

E

TM

TIMING

CONTROL

R

MAG PICKUP

INSTALLATION INSTRUCTIONS 3

DIAGRAMS

The following wiring diagrams show common installations.

NOTE: The MSD 5 and Blaster Ignitions
are inductive designs and do not share
the same wiring as the 6-Series Ignitions.

Figure 5 Wiring to a Points or Amplifier Ignition with an MSD 5 or Blaster Ignition using the Points Trigger.

ORIGINAL COIL+ WIRE

FROM IGNITION

KEY

BLACK

ORANGE

HEAVY RED

HEAVY BLACK

RED

TO BATTERY+

TO BATTERY-

GRAY

DIGITAL 6A

TACH OUTPUT

POINTS

OR AMPLIFIER

DISTRIBUTOR

WHITE

GREEN (-)

ORIGINAL

COIL WIRE

-

RED

YELLOW

VIOLET (+)

MAG PICKUP

MAGNETIC PICKUP

BLACK

TO GROUND

(NOT USED)

NOT USED

WHITE

INDICATES CONNECTION USING

WIRE SPLICE DEVICE

TIMING

CONTROL

A

D

C

V

A

N

E

TM

TIMING

CONTROL UNIT

Figure 6 Wiring to Points or Amplifier Ignition with an MSD 6 Series.

M S D   •   W W W . M S D P E R F O R M A N C E . C O M   •   ( 9 1 5 )   8 5 7 - 5 2 0 0   •   F A X   ( 9 1 5 )   8 5 7 - 3 3 4 4