MSD 6421 Installation

MSD 6AL-2 Ignition Control

PN 6421

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Parts Included:

1 - MSD Ignition 1 - Screwdriver 4 - Vibration Mounts
1 - Harness, PN 8860 1 - Parts Bag, ASY 28928

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

OPERATION AND FEATURES

DIGITAL OPERATION

The MSD 6AL-2 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 6AL-2 have been thoroughly filtered to create protection against Electro
Magnetic Interference (EMI).

CAPACITIVE DISCHARGE

The MSD 6AL-2 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 3,000 rpm there is simply not enough “time” to fire the spark plug more than once,
so there is only one powerful spark.

PROTECTION

The MSD 6AL-2 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 the trigger signals and will
flash to warn if the supply voltage drops below 9 volts while under 3,000 rpm.

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2

INSTALLATION INSTRUCTIONS

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 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 6AL-2 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 seven 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 .9 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 6AL-2 Ignition can be used with most stock coils and aftermarket coils designed to replace
the stock coils. The line of MSD Blaster Coils, PN 8202, PN 8207 and PN 8222, are great for street
and mild racing. For extended high rpm operation the Blaster HVC, PN 8252 or HVC II, PN 8253,
are recommended. For more information on recommended coils, check with our Customer Service
Department at [phone].

TACHOMETERS

The MSD Ignition features a Gray Tach Output wire that provides a trigger signal for tachometers, a
shift light or other add-on rpm activated devices. The Tach Output wire produces a 12 volt square
wave signal with a 25° 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.
If your GM vehicle has an in-line filter it may cause the tach to drop to zero on acceleration. If this
occurs, bypass the filter.

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 or Street Fire 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.

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INSTALLATION INSTRUCTIONS

3

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: 0.035" - 0.045"

10.5:1 - 13.0:1: 0.030" - 0.035"
Above 13.0:1: 0.025" - 0.030"

Note: Close the spark plug gap down as compression increases.

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 glove box.
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 a 3/16" bit to drill holes, install the vibration mounts and
mount the ignition.

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4

WIRING

INSTALLATION INSTRUCTIONS

Power Leads

Heavy Red

Heavy Black

Red

Orange

Black

Trigger
Wires

White

White/Blue

Violet
and Green
(Magnetic
Pickup
Connector)

These are the two heavy 14 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 28 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 three circuits that can be used to trigger the MSD Ignition;
a Points circuit (the White wire), a Magnetic Pickup circuit (the Green
and Violet wires), and a Hall-effect wire (White/Blue). Only one circuit
will be used at a 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 White/Blue wire and Magnetic Pickup
connector are not used.

Hall-effect Trigger. This wire connects to the trigger wire of a Hall­effect pickup. When used, the White and Magnetic Pickup wires

are 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 or White/Blue wires are not.

Accessories

Blue

Gray

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.

Tach output wire. Connects to the tachometer trigger wire or other
rpm activated device.

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 (12 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

5

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

The MSD is programmed for operation on 8-cylinder engines.

CYLINDER

COUNT

If installing the Ignition on a different style engine, the number
of cylinders will need to be selected on the Cylinder Select

4

6

8

CYL

Rotary Switch (Figure 1).

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 2). Note: The engine can be running as
you make adjustments to the rev limiter 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 11,900 rpm. Setting both dials
to Zero defaults to a limit of 10,000 rpm. Setting the 1,000's dial to 1 defaults to 11,000 rpm rev limit.

THIS EXAMPLE
SHOWS 2,500
RPM.

THIS EXAMPLE
SHOWS THE
OVERREV AT
6,500.

Figure 1 Programming the Number of

Cylinders.

THIS EXAMPLE
SHOWS 8-CYLIN­DER ENGINE (FULL
CLOCKWISE).

6

4

8

CYL

Figure 2 Adjusting the Rev Limits.

Figure 2 Rev Limiter sample setting.

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6

INSTALLATION INSTRUCTIONS

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 1,000 to 9,900 and will default to
1,000 rpm if the dials are set to an rpm

TO TRANS-BRAKE

OR LINE-LOCK SOLENOID

TO 12V

BLUE

below this range. An example of wiring
the 2-Step Limit so it is activated with the
line-lock is shown in Figure 3.

Figure 3 Wiring the 2-Step Rev Limit.

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.

• Conrm 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

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 above idle speeds when everything is functioning properly.

• Flashes once per second if the battery supply voltage is low when under 3,000 rpm (while

multiple sparking). This indicates a charging problem or poor connection.

• It will ash approximately once per second if the battery input voltage is above 28 volts for

a sustained amount of time.

• The LED will ash 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 or White/Blue 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 4 lists common tachometers
and if an Adapter is necessary.

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INSTALLATION INSTRUCTIONS

ATTACH DIODE TO TERMINAL "1"

CHARGING

LIGHT

Tachometer Compatibility List

7

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 Wire on the MSD 6AL-2 Ignition.

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

WHITE WIRE TRIGGER MAGNETIC TRIGGER CONNECTOR

Figure 4 Common Tachometers and Adapters.

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 Gray tach wire 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 5.

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

Figure 5 Wiring the Dual Ballast Resistor.

EARLY GM VEHICLES
ATTACH DIODE TO TERMINAL "4"

1 2 3 4

1A-100V DIODE

FORD VEHICLES

SPLICE HERE

TO

Figure 6 Installing the diode to a GM or Ford Vehicle.

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8

SMALLER OF THE 2-WIRES

DIODE

WIRE LOOM

GM 2-WIRE ALTERNATORS

INSTALLATION INSTRUCTIONS

from the battery, it does not require much current to keep the unit energized. If you are experiencing run­on, 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 6 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 (
shown in Figure 6

).

as

Ford: Install the Diode in-line 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

7). It is usually a Brown wire.

Figure 7 Installing the Diode to a

1973-1983 GM Vehicle.

Most other applications: On
other applications where engine

MSD

Run-On is experienced, a
Resistor can be put in-line
to the MSD's small Red wire
(Figure 8). This resistor will keep
voltage from leaking through to
the MSD unit.

Figure 8 Wiring the Dual Ballast Resistor for Run-On.

MISSES AND INTERMITTENT PROBLEMS

Experience at the races has shown that if your engine is experiencing a miss or hesitation at higher
rpm, it is usually not directly ignition. Most probable causes include faulty wiring, a coil or plug wire
failure, arcing from the cap or boot plug to ground or spark ionization inside the cap. Several items
to inspect are:

• Always inspect the plug wires at the cap and at the plug for a tight connection and visually inspect

for cuts, abrasions or burns.

• Inspect the Primary Coil Wire connections. Because the MSD is a Capacitive Discharge ignition and it

receives a direct 12 volt source from the battery, there will not be any voltage at the Coil Positive (+)
terminal even with the key turned On. During cranking or while the engine is running, very high voltage
will be present and no test equipment should be connected.

WARNING: Do not touch the coil terminals during cranking or while the engine is running.

• Make sure that the battery is fully charged and the connections are clean and tight. If you are not

running an alternator this is an imperative check. If the battery voltage falls below 9 volts during a
race, the MSD output voltage will drop and the current draw will increase.

• Is the engine running lean? Inspect the spark plugs and complete fuel system.

• Inspect all wiring connections for corrosion or damage. Remember to always use proper connections

followed by soldering and seal the connections completely.

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INSTALLATION INSTRUCTIONS

WHITE OR WHITE/BLUE

WIRE

GROUND

GREEN

VIOLET

JUMPER

WIRE

9

If everything checks positive, use the following procedure to test the ignition for spark. MSD also
offers an Ignition Tester, PN 8998 or PN 8996. This tool allows you to check your complete ignition
system while it is in the car as well as the operation of rpm limits, activated switches and shift lights.

CHECKING FOR SPARK

WHITE WIRE TRIGGER

If triggering the ignition with the White or White/Blue
wire:

1. Make sure the ignition switch is in the “Off” position.

2. Remove the coil wire from the distributor cap and
set the terminal approximately 1/2" from ground.

3. Disconnect the MSD trigger wire (White or White/
Blue) from the distributor.

4. Turn the ignition to the On position. Do not crank
the engine.

5. Tap the White wire to ground several times. Each
time you pull the wire from ground, a spark should
jump from the coil wire to ground. If spark is

Figure 9 Checking for Spark with the White Wire.

present, the ignition is working properly. If there
is no spark skip to step 6.

MAGNETIC PICKUP TRIGGER

If triggering with the Magnetic Pickup:

1. Make sure the ignition switch is in the “Off” position.

2. Remove the coil wire from the distributor cap and

set the terminal approximately 1/2" from ground.

3. Disconnect the MSD magnetic pickup wires from

the distributor.

4. Turn the ignition to the On position. Do not crank

the engine.

5. With a small jumper wire, short the MSD’s Green

and Violet magnetic pickup wires together several

Figure 10 Checking for Spark with the Mag Pickup.

times. Each time you break this short, a spark
should jump from the coil wire to ground. If spark
is present, the ignition is working properly. If there is no spark skip to step 6.

6. If there is no spark:

A. Inspect all of the wiring.
B. Substitute another coil and repeat the test. If there is now spark, the coil is at fault.
C. If there is still no spark, check to make sure there are 12 volts on the small Red wire from the

MSD when the key is in the On position. If 12 volts are not present, find another switched 12
volt source and repeat the test.

D. If, after following the test procedures and inspecting all of the wiring, there is still no spark, the

MSD Ignition is in need of repair. See the Warranty and Service section for information.

The following wiring diagrams illustrate numerous installations on different vehicles and applications.
If you experience difficulties when installing your MSD, contact our Customer Support Department at
[phone] (7 - 5 Mountain time) or e-mail us at: [e-mail]

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