MSD 89501 Installation
MSD RPM Activated Switch
PN 89501 - 1-Cylinder, 4 Stroke 720°
PN 89502 - 2-Cylinder, 4 Stroke 360°
1-Cylinder, 2 Stroke 360°
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Important: Read the instructions before attempting the installation.
Parts Included In This Kit:
1 - RPM Switch
4 - Self Tapping Screws
Note: RPM Modules must be purchased separately. See the chart on page 4 for part numbers.
PN 89501, 1-CYLINDER, 4-STROKE (720°) ENGINES
This RPM Switch is preset for an ignition trigger, that fires every 720° of crankshaft rotation. This
particular Switch may not be programmed for any other configurations. This unit is typically used on
a multiple cylinder engine, which has a Coil-per-Cylinder ignition system.
PN 89502, 2-CYLINDER, 4-STROKE (360°) ENGINES OR 1-CYL, 2-STROKE (360°)
4 - Heat Shrink Caps
This RPM Switch is preset for an ignition trigger that fires every 360° of crankshaft rotation. This
particular Switch may not be programmed for any other configuration. This unit is typically used on
a waste spark ignition system equipped with a dual tower coil that fires two cylinders. This coil is
triggered every 360° of crankshaft rotation. This RPM Switch may also be used on a single cylinder,
2-Stroke engine.
Note: If an MSD Ignition is used in conjunction with an RPM Switch an alternate RPM Switch may
be needed.
The RPM Activated Switch can be connected to stock ignition systems or an MSD Ignition. When
using a capacitive discharge ignition such as an MSD, do not connect the Switch to the coil negative
terminal. Damage to the Switch will occur.
The Switch is capable of carrying 1.5 amps of current. If the circuit you are activating requires more
current, an MSD Relay, PN 8960 or PN 8961 must be used. The MSD RPM Activated Switch is
equipped with a “smart driver”. This circuit will protect the RPM Switch from damage by monitoring
its temperature. If there is an inadvertent short or too much current is drawn through the Switch,
the smart driver will sense the increase in temperature and shut the Switch off. However, once the
temperature drops to a safe point, the smart driver will turn the Switch back on. It will continuously
cycle On and Off as the temperature dictates.
If you experience a problem with your Switch not operating, turn the circuit off for a few minutes to
cool then try again. If the circuit activates then shuts off, there may be too much current flow. Check
the device's Installation Instructions to find its recommended maximum current.
The RPM Switch has two activation wires. The Yellow wire is Normally Open and will activate a circuit
by switching to ground. The Gray wire is Normally Closed to ground and will open the ground circuit
at the desired RPM (Figure 1). If no RPM module is installed, the Switch will not activate the circuit.
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2 INSTALLATION INSTRUCTIONS
Figure 1 Operation of the RPM Activated Swtich.
MOUNTING
The Switch may be mounted under the hood as long as it is away from direct engine heat sources.
Keep in mind that the rpm modules should be easy to access for changes. The Switch can be
mounted with the double-sided tape or with the four self tapping screws supplied. Use the Switch
as a template and mark the mounting hole locations. Remove the Switch and drill the holes using
a 3/16" drill bit then install the screws.
WIRING
Red Connects to a switched 12 volt source.
Black Connects to ground.
White The rpm input wire. With an MSD Ignition, this connects to the Tach Output terminal.
Yellow This is an activation wire and is Normally Open and will switch to ground. It connects
Gray This is an activation wire and is Normally Closed to ground. It will open the ground
path of a circuit.
On inductive ignitions, it connects to the coil negative terminal.
to the ground side of the device you plan to activate.
Figure 2 Wiring to a 4-Cylinder, Coil-per-Cylinder Ignition.
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