MSD 6520 Installation

INSTALLATION INSTRUCTIONS

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MSD Digital 6 Plus Ignition Control

PN 6520

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Parts Included:

1 - MSD Ignition 1 - Harness, PN 8860 1 - Parts Bag, ASY 19864

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

the Negative cable first and install it last.

Note: Solid Core spark plug wires cannot be used with an MSD Ignition.

Important: When installing a Digital Series Ignition, the timing must be checked and reset to your engine's

specifications.

REV LIMITER

This Ignition features a built-in Soft Touch Rev Control with two different rpm limits. The Soft Touch circuitry
provides a smooth and accurate rev limit by dropping the spark to individual cylinders. The Soft Touch
produces a load-free rev limit that is within 1% of the selected rpm.
You can select two rev limits; one for a low limit that can be used when staging the car, and another limit
for top end overrev protection. Both rpm limits are adjusted in 100 rpm increments with the sealed rotary
switches on the side of the ignition. Using and programming the Two Step is explained in detail on page 6.

OPERATION AND FEATURES

Note: Do not use digital or dial back timing lights.

DIGITAL OPERATION

The MSD Digital 6 Plus uses a high speed RISC microcontroller to control the ignition’s output while
constantly analyzing the various inputs such as supply voltage, trigger signals and rpm. The high speed
controller can make extremely quick compensations to the output voltage, multiple spark series, timing and
rpm limits while maintaining accurate timing signals to within 1° and 1% of the rpm limits. The circuits and
controller of the Digital 6 Plus have been thoroughly debounced and isolated to create protection against
Electro Magnetic Interference (EMI).

CAPACITIVE DISCHARGE

The MSD Digital 6 Plus features a capacitive discharge ignition design. The majority of stock ignition systems
are inductive ignitions. In an inductive ignition, the coil must store and step up the voltage to maximum
strength in between each firing. At higher rpm, since there is less time to charge the coil to full capacity, the
voltage falls short of reaching maximum energy which results in a loss of power or top end miss.
The MSD Ignition features a capacitor which is quickly charged with 520 - 535 volts and stores it until the
ignition is triggered. With the CD design, the voltage sent to the coil is always at full power even at high rpm.

MULTIPLE SPARKS

The MSD produces full power multiple sparks for each firing of a plug. The number of multiple sparks that
occur decreases as rpm increases, however the spark series always lasts for 20° of crankshaft rotation.
Above 3,300 rpm there is simply not enough “time” to fire the spark plug more than once, so there is only
one powerful spark.

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 4M 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

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INSTALLATION INSTRUCTIONS

PROTECTION

The MSD Digital 6 Plus has a built in reverse polarity protection circuit. This will protect the ignition in the
event of wrong connections. It will also shut off for protection from a surge in power. The ignition will still
operate once the surge or polarity is corrected.

LED INDICATOR

There is an LED that monitors the status of the Ignition. The LED monitors several parameters of the
ignition including trigger signal, low voltage and high voltage.

RETARD CONTROL

There is a single stage of retard that can be adjusted from 0 to 9.9 degrees in 1/10° increments. The retard
is activated when the Pink wire receives 12 volts which is explained on page 6.

START RETARD

To ease starting on engines with locked out timing, there is a Start Retard circuit. When set, the timing will
be retarded 20° until the engine reaches over 800 rpm. Activating the Start Retard is done with the Cylinder
Select dial and is explained on page 5.

CYLINDER SELECT

The MSD is programmed at the factory for use on 8-cylinder engines. If you are installing it to a different
engine you will have to program the Ignition. This is easily achieved through the cylinder select switch on
the side of the ignition. Page 5 outlines setting the cylinder select.

GENERAL INFORMATION

BATTERY

An MSD 6 Series Ignition Control will operate on any negative ground, 12 volt electrical system with a
distributor. The MSD can be used with 16 volt batteries and can withstand a momentary 24 volts in case of
jump starts. The Ignition will deliver full voltage with a supply of 9 - 18 volts and will operate with a supply
voltage as low as six volts.
If your application does not use an alternator, allow at least 15 amp/hour for every half hour of operation.
The MSD uses about .7 Amps for every 1,000 rpm. If the engine is cranked with the same battery or other
accessories such as an electric fuel or water pump are used, the amp/hour rating should be higher.

COILS

The MSD Digital 6 Plus Ignition can be used with most stock coils and aftermarket coils designed to replace
the stock coils. The line of MSD Blaster Coils are great for street and mild racing. For extended high rpm
operation the Blaster HVC, PN 8252, is recommended. For more information on recommended coils,
consult the supplied Coil Application Chart or check with our Customer
Service Department at [phone].

TACHOMETERS

The MSD Ignition features a Tach Output Terminal on the side of the unit
(Figure 1). This terminal provides a trigger signal for tachometers, a shift light
or other add-on rpm activated devices. The Tach Output Terminal produces
a 12 volt square wave signal with a 30° duty cycle.
Some vehicles with factory tachometers may require a Tach Adapter to
operate with the MSD. For more information on Tachometers and MSD
Tach Adapters, see the Tachometer Section on page 7.

Figure 1 Tach Terminal

If your GM vehicle has an inline filter it may cause the tach to drop to zero on acceleration. If this occurs,
bypass the filter.

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INSTALLATION INSTRUCTIONS

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SPARK PLUGS AND WIRES

Spark plug wires are very important to the operation of your ignition system. A good quality, helically wound
wire and proper routing are required to get the best performance from your ignition, such as the MSD Heli­Core or 8.5mm Super Conductor Wire. Helically wound wires provide a good path for the spark to follow
while keeping Electro Magnetic Interference (EMI) to a minimum. Excessive EMI, such as the amount that
solid core wires produce, will interfere with the operation of the MSD. Solid Core spark plug wires cannot

be used with an MSD Ignition.

Routing: Correct routing of the plug wires is also important to performance. Wires should be routed away

from sharp edges and engine heat sources. If there are two wires that are next to each other in the engine’s
firing order, the wires should be routed away from each other to avoid inducing a spark into the other wire.
For example, in a Chevy V8, the firing order is 1-8-4-3-6-5-7-2. The #5 and #7 cylinders are next to each
other in the engine and in the firing order. If the voltage from the #5 wire is induced into #7 detonation
could occur and cause engine damage.
To add more heat protection to your plug wires, MSD offers Pro-Heat Guard, PN 3411. This is a glass woven
and silicone coated protective sleeve that you slide over your plug wires. For extra protection of the spark
plug boots, MSD offers Pro Boot Guard, PN 3412.

Spark Plugs: Choosing the correct spark plug design and heat range is important when trying to get the
best performance possible. Since there are so many engine combinations and manufacturers, MSD does
not recommend which plug or gap is exactly right for your application.
It is recommended to follow the engine builder or manufacturer’s specification for spark plugs. With that,
you can then experiment with the plug gap to obtain the best performance. The gap of the plugs can be
opened in 0.005" increments, then tested until the best performance is obtained. MSD judges the plug gap
by compression and components.

These examples are just starting points to get you going in
the right direction. Every application is different and should
be tested and tuned.

Compression Spark Plug Gap
Up to 10.5:1: 0.050" - 0.060"

10.5:1 - 13.0:1: 0.040" - 0.050"
Above 13.0:1: 0.035" - 0.045"

Welding: If you are welding on your vehicle, to avoid the chance of damage, always disconnect both Heavy
Power cables of the MSD (You should also disconnect the tach ground wire too).

Distributor Cap and Rotor: It is recommended to install a new distributor cap and rotor when installing
the MSD Ignition Control. The cap should be clean inside and out especially the terminals and rotor tip. On
vehicles with smaller caps, it is possible for the air inside the cap to become electrically charged causing
crossfire which can result in misfire. This can be prevented by drilling a couple vent holes in the cap.
The holes should be placed between the terminals, at rotor height and face away from the intake. If your
environment demands it, place a small piece of screen over the hole to act as a filter.

MOUNTING

The MSD can be mounted in the engine compartment as long as it is away from direct engine heat sources.
It is not recommended to mount the unit in an enclosed area such as the glovebox.
When you find a suitable location to mount the unit, make sure the wires of the ignition reach their
connections. Also be sure that the program dials can be accessed. Hold the Ignition in place and mark the
location of the mounting holes. Use an 1/8” bit to drill the holes or, if using the supplied vibration mounts,
use a 3/16” bit and mount the ignition.

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WIRING

INSTALLATION INSTRUCTIONS

Power Leads

Heavy Red

Heavy Black

Red

Orange

Black

Trigger
Wires

White

Violet
and Green
(Magnetic
Pickup
Connector)

Green Loop

Accessories
Blue

These are the two heavy 12 gauge wires and are responsible for
getting direct battery voltage to the ignition. The Ignition is load
protected from reverse battery connections and will automatically
shut down if there is over 27 volts input.
This wire connects directly to the battery positive (+) terminal or a
positive battery junction such as the starter solenoid. Note: Do not
connect to the alternator.
This wire connects to a good ground, either at the battery negative
(-) terminal or to the engine.

This wire is responsible for turning the MSD On and Off. Connects to
a switched 12 volt source such as the ignition key or switch.

This wire connects to the coil positive (+) terminal. This is the ONLY
wire that makes electrical contact with the positive coil terminal.

This wire connects to the coil negative (-) terminal. This is the ONLY
wire that makes electrical contact with the negative coil terminal.

There are two circuits that can be used to trigger the MSD Ignition;
a Points circuit (the White wire) and a Magnetic Pickup circuit (the
Green and Violet wires). The two circuits will never be used at the
same time.

This wire is used to connect to breaker points, electronic ignition
amplifier output or to the Yellow wire of an MSD Timing Accessory.

When this wire is used, the Magnetic Pickup connector is not
used.

These wires are routed together in one harness as the magnetic pickup
connector. The connector plugs directly into an MSD distributor or
crank trigger. It will also connect to aftermarket pickups. The Violet
wire is positive (+) and the Green wire is negative (-). When these
wires are used, the White wire is not.

This wire loops out of the strain relief. It is used to compensate for
different magnetic pickups. The MSD is set up to be used with GM
distributor and MSD crank triggers. If you are installing the ignition
with an MSD Distributor or Ford Distributor, this Loop should be cut
and sealed.

This wire activates the Two Step Rev Control. When 12 volts is applied
to this wire, the low rpm limit is activated. When 12 volts is removed,
the rev limit returns to the high limit.

Pink

This wire activates the retard stage when it is applied to 12 volts. When
12 volts is removed the retard is deactivated.

GENERAL WIRING INFORMATION

Wire Length: All of the wires of the MSD Ignition may be shortened as long as quality connectors
are used or soldered in place. To lengthen the wires, use one size bigger gauge wire (10 gauge for
the power leads and 16 gauge for the other wires) with the proper connections. All connections must
be soldered and sealed.

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INSTALLATION INSTRUCTIONS

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Grounds: A poor ground connection can cause many frustrating problems. When a wire is specified
to go to ground, it should be connected to the battery negative terminal, engine block or chassis.
There should always be a ground strap between the engine and the chassis. Always securely connect
the ground wire to a clean, paint free metal surface.

Ballast Resistor: If your vehicle has a ballast resistor in line with the coil wiring, it is recommended
to bypass it.

Routing Wires: The MSD wires should be routed away from direct heat sources such as exhaust
manifolds and headers and any sharp edges. The trigger wires should be routed separate from the
other wires and spark plug wires. It is best if they are routed along a ground plane such as the block
or firewall which creates an electrical shield. The magnetic pickup wires should always be routed
separately and should be twisted together to help reduce extraneous interference.

PROGRAMMING

CYLINDER SELECT

Cylinder Select Cyl.Select w/ 20° Start Retard
0 = 4 cyl. 4 = 4 cyl.
1 = 6 cyl. 5 = 6 cyl.
2 = 8 cyl. 6 = 8 cyl.
3 = 6 odd 7 = 6 odd fire

The MSD is programmed for operation
on 8-cylinder engines. If installing the
Ignition on a different style engine, the
number of cylinders will need to be
selected on the Cylinder Select Rotary
Switch (Figure 2).

START RETARD

Note: Positions 8 and
9 cause the ignition
NOT to run. Use as a
theft deterrant.

Figure 2 Programming the Number of Cylinders.

The Start Retard will be activated during
cranking only when the Cylinder Select
dial is in the 4, 5, 6 or 7 position (Figure 2). During cranking the timing will retard 20° until 800 rpm when it
returns to the mechanical setting. If engine speed drops below 500 rpm, the start retard is activated again.

MAGNETIC PICKUP COMPENSATION

Note: If your application uses the MSD's White wire for the trigger input, the magnetic compensation circuit

is not used.

The Green wire loop of the MSD provides a timing compensation for different style trigger pickups. Having the
ability to program for the style pickup being used provides a more accurate timing signal. This compensation
is used primarily with crank trigger or locked out timing applications.
The Digital MSD is programmed at the factory for use with an MSD Crank Trigger or GM magnetic pickup.
If you are using an MSD Billet Distributor or the magnetic pickup of a Ford or Chrysler distributor the Green
Loop should be cut and sealed (Figure 3).

Note: It is recommended to check your total timing to ensure the setting for your application.

GREEN LOOP

CUT LOOP DO NOT CUT

MSD Distributors Points
Factory Ford Electronic Amplifiers
Chrysler GM HEI
MSD Crank Trigger

Figure 3 Programming the Compensation Circuit.

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(Stock, Mallory, Accel)

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INSTALLATION INSTRUCTIONS

REV LIMITER

There are two adjustable rev limits that you can adjust; the Max Limit and the Two Step Limit. Both limits are
adjusted in 100 rpm increments by turning the rotary switches on the side of the Ignition (Figure 4). Note:
The engine can be running as you make adjustments to the rev limiter and retard function.

Max Limit: This is the overrev rpm limit. The Soft Touch circuitry will begin dropping the spark to cylinders
any time the rpm reaches the amount you select, except if the Two Step Limit is activated (12 volts applied
to the Blue wire). The limit can be adjusted from 2,000 to 9,900 rpm. Setting both dials to Zero defaults to
a limit of 12,500 rpm.

Figure 4 Adjusting the Rev Limits.

2-Step Limit: This rpm limit is activated
when 12 volts are applied to the Blue
wire. When activated, this limit overrides
the Max Limit. This limit is adjustable from
2,000 to 9,900 and will default to 2,000 rpm
if the dials are set to an rpm below this
range. An example of wiring the 2-Step
Limit so it is activated with the line-lock is
shown in Figure 5.

RETARD STAGE

The MSD features a single stage retard
step that is activated when 12 volts are
applied to the Pink wire. The retard will
remain until the 12 volts are removed.
This retard step can be connected to
a nitrous solenoid activation wire or
micro-switch on the shifter. The retard
is adjustable from 0° to 9.9° in 1/10°
increments. The example in Figure
6 shows connecting the retard to a
nitrous stage.

Figure 5 Wiring the 2-Step Rev Limit.

Figure 6 Wiring the Retard Stage.

Note: This retard will only operate
above 2,000 rpm.

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INSTALLATION INSTRUCTIONS

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PRESTART CHECK LIST

• The only wires connected to the coil terminals are the MSD Orange to coil positive and Black to coil negative.

• The small Red wire of the MSD is connected to a switched 12 volt source.

• Confirm the cylinder select is in the proper position for your application.

• The MSD power leads are connected directly to the battery positive and negative terminals.

• The battery is connected and fully charged if not using an alternator.

• The engine is equipped with at least one ground strap to the chassis.

TROUBLESHOOTING

Every MSD Ignition undergoes numerous quality control checks including a four hour burn-in test. If you
experience a problem with your MSD, our research has shown that the majority of problems are due to
improper installation or poor connections.
The Troubleshooting section has several checks and tests you can perform to ensure proper installation
and operation of the MSD. If you have any questions concerning your MSD, call our Customer Support
Department at [phone], 7 - 6 mountain time.

LED

The LED on the side of the MSD monitors several operating conditions of the MSD. If the LED indicates that
there is a problem with the ignition system, follow the steps through the Troubleshooting section. The LED
will appear to be on steady at above idle speeds when everything is functioning properly.

• Flashes once per second if the battery supply voltage is low when under 3,300 rpm (while
multiple sparking). This indicates a charging problem or poor connection.

• It will flash approximately once per second if the battery input voltage is above 27 volts for
a sustained amount of time.

• The LED will flash for every trigger signal from the distributor or crank trigger. You can take
advantage of this when statically setting the timing when using the White wire to trigger.

TACH/FUEL ADAPTERS

If your tachometer does not operate correctly or if you experience a no-run situation with your foreign
vehicle you probably need an MSD Tach Adapter. The chart in Figure 7 lists common tachometers and if
an Adapter is necessary.

Tachometer Compatibility List

AFTERMARKET TACHOMETER

AUTOGAGE 8910 8920

AUTOMETER NONE NONE
FORD MOTORSPORTS NONE NONE
MALLORY NONE NONE
MOROSO NONE NONE
STEWART (voltage triggered) 8910 8920
S.W. & BI TORX NONE NONE
SUN 8910 8920
VDO NONE NONE
AMC (JEEP) 8910 8920
CHRYSLER 8910 8920
FORD (voltage triggered) 8910 8920
GENERAL MOTORS Bypass In-Line Filter Bypass In-line filter

IMPORTS 8910 8920
Note:

Tach Output Terminal on the MSD 6 Series Ignition Unit using the supplied Female Faston Receptacle.

On the list above, the trigger wire on tachometers that are marked NONE may be connected to the

WHITE WIRE TRIGGER

Figure 7 Common Tachometers and Adapters.

MAGNETIC TRIGGER CONNECTOR

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INSTALLATION INSTRUCTIONS

NO-RUN ON FOREIGN VEHICLES

Some foreign vehicles with fuel injection systems may require an MSD Tach/Fuel Injection Adapter to run
with an MSD 6 Series Ignition. This is because many of these systems use the same trigger source to
operate the MSD, the tachometer and the fuel injection. This results in a voltage signal that is too low to
accurately trigger the fuel injection. To fix this, an MSD Tach Adapter, PN 8910, will remedy the problem
on the majority of vehicles. If the PN 8910 does not fix the problem, the PN 8910-EIS will be required.

Note: Toyotas and Ford Probes will require the PN 8910-EIS Adapter.

INOPERATIVE TACHOMETERS

If your tachometer fails to operate with the MSD installed you may need an MSD Tach Adapter. Before
getting an Adapter, try connecting your tachometer trigger wire to the tach output terminal on the side
of the MSD. This output produces a 12 volt, square wave (see page 2). If the tach still does not operate,
you will need a Tach Adapter. There are two Tach Adapters:

PN 8920: If you are using the Magnetic Pickup connector (Green and Violet wires) to trigger the MSD,
you will need the PN 8920.

PN 8910: If your tachometer was triggered from the coil negative terminal (voltage trigger) and you are
using the White wire to trigger the MSD you will need the PN 8910.

BALLAST RESISTOR

If you have a current trigger tach (originally coil positive)
and use the White wire of the MSD, you can purchase a
Chrysler Dual Ballast Resistor (used from 1973 - 1976) and
wire it as shown in Figure 8.

ENGINE RUN-ON

If your engine continues to run even when the ignition is
turned Off you are experiencing engine Run-On. This usually
only occurs on older vehicles with an external voltage
regulator. Because the MSD receives power directly from
the battery, it does not require much current to keep the unit
energized. If you are experiencing run-on, it is due to a small
amount of voltage going through the charging lamp indicator
and feeding the small Red wire even if the key is turned off.

Early Ford and GM: To solve the Run-On problem, a Diode
is supplied with the MSD in the parts bag. By installing this
Diode in-line of the wire that goes to the Charging indicator,
the voltage is kept from entering the MSD. Figure 9 shows the proper
installation for early Ford and GM vehicles.

Note: Diodes are used to allow voltage to flow only one way. Make

sure the Diode is installed facing the proper direction (
in Figure 9

).

Ford: Install the Diode inline to the wire going to the “1” terminal.
GM: Install the Diode in-line to the wire going to terminal #4.
GM: 1973 - 1983 with Delcotron Alternators
GM: Delcotron Alternators use an internal voltage regulator. Install the

Diode in-line on the smallest wire exiting the alternator (Figure 10). It
is usually a Brown wire.

Figure 8 Wiring the Dual Ballast Resistor.

Figure 9 Installing the diode to a GM or Ford Vehicle.

as shown

Figure 10 Installing the Diode to a

1973-1983 GM Vehicle.

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