Owners manual

INSTALLATION INSTRUCTIONS 13
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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 1). 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 13.
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 14 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 (as shown in Figure 14).
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.
Figure 14 Installing the Diode to fix Run-On.
1A-400V DIODE
TO CHARGING
LIGHT
SPLICE HERE
OR
DELCOTRON
ALTERNATOR
FORD VEHICLES
ATTACH DIODE TO
TERMINAL "1"
EARLY GM VEHICLES ATTACH DIODE TO TERMINAL "4"
1 2 3 4
SMALLER OF THE 2-WIRES
DIODE
WIRE LOOM
GM 2-WIRE ALTERNATORS
FROM POINTS
OR AMPLIFIER
MSD WHITE
MSD RED
SWITCHED 12V
(original coil+ wire from tach)
CHRYSLER DUAL
BALLAST RESISTOR
Figure 13 Wiring the Dual Ballast Resistor.