MSD 8956 Installation

MSD RPM Activated Window Switch

PN 8956

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IMPORTANT: Read the instructions before attempting the installation.

Parts Included

1 - RPM Window Switch
4 - Self Tapping Screws

Note: RPM Modules must be purchased separately. See the chart on the last page for part
numbers.

The RPM Activated Window Switch can be connected to stock ignition systems or MSD Ignitions. When
using a capacitive discharge ignition such as an MSD, do not connect the Switch to the coil negative
terminal. Damage to the Switch may occur.

The Switch is capable of carrying 1.5 amps. If the circuit you are activating requires more current, an
MSD Relay, PN 8960 or 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
inadvertant short or too much current is drawn through the Switch, the smart driver will sense the increased
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.

4 - Heat-Shrink Caps

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 Window Switch has a circuit that activates a device by providing a ground path at a desired
rpm (Figure 1). The ground will be removed at a different rpm to deactivate the device. If no rpm
module is installed, the device will remain activated as long as the rpm is above the activation amount.

Figure 1 Operation of the RPM Window Switch.

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 4

2 INSTALLATION INSTRUCTIONS

CYLINDER PROGRAMMING

The Window Switch is programmed for 8-cylinder applications, however it can be used with 4 or
6-cylinder applications. To program the Switch for different applications, the cylinder select loops
must be modified as shown in Figure 2. After cutting a wire loop, seal the wire end with the supplied
head-shrink caps. Use a heat gun or other heat source to shrink the cap for a good seal.

CYLINDERS CUT LOOPS

8 NONE
6 RED
4 RED & BLUE

Figure 2 Cylinder Select Loops.

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.

On inductive ignitions, it connects to the coil negative terminal.

Yellow This is the circuit ground wire (normally open switch to ground). It connects to the
ground side of the device you plan to activate.

Note: Inductive ignitions only.

Figure 3 Wiring to an Inductive Ignition System.

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 4