MSD 8950 Installation

MSD RPM Activated Switch

PN 8950

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IMPORTANT: Read the instructions before attempting the installation.

Parts Included:

1 - RPM Switch 4 - Heat-Shrink Caps
4 - Self Tapping Screws

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

The RPM Activated 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.

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.

Figure 1 Operation of the RPM Activated 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

SEAL THE LOOP ENDS

HEAT-SHRINK

CAP

CYLINDER LOOP

CYLINDER PROGRAMMING

The 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 heat-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

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 an activation wire and is Normally Open and will switch to ground. It connects

to the ground side of the device you plan to activate.

Gray This is an activation wire and is Normally Closed to ground. It will open the ground

path of a circuit.

Note: Inductive ignitions only.

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

Figure 3 Wiring to an Inductive Ignition System.