MSD 6520 Digital 6-Plus Ignition Control Installation - Manual (Page 8)

8 INSTALLATION INSTRUCTIONS
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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
Figure 8 Wiring the Dual Ballast Resistor.
Figure 9 Installing the diode to a GM or Ford Vehicle.
Figure 10 Installing the Diode to a
1973-1983 GM Vehicle.
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 (as shown
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.