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MALLORY TECHNICAL SUPPORT

(775) 882-6600

tech@mrgasket.com

®

WINDOW RPM ACTIVATED SWITCH

PART NO. 646

INSTALLATION INSTRUCTIONS

FORM 1008 (REV. A) 01/02

GENERAL INFORMATION

The Mallory 646 Window RPM Switch is an RPM switch that is triggered

from the tach terminal available on most aftermarket performance ignitions.

It will not only activate at a particular RPM, but can also be set to de-

activate at a second, higher, RPM. It can be used on 4-12 cylinder engines.

NOTE: The Mallory 646 CANNOT be triggered from points or elec-

tronic distributor. It must be triggered from a tach output terminal.

The 646 features two independent sets of switch contacts that switch other

devices on or off when the selected RPM is reached. These contacts

switch a maximum current of 5 amps. To switch more than 5 amps, you

must use the RPM Activated Switch output to drive a high current relay,

such as a horn or headlight (see illustrations).

NOTE: The switch contacts are NOT connected electrically. This

allows you to turn one circuit on and another off at the same RPM.

MOUNTING PROCEDURE

Step 1

Disconnect the battery (–) cable to cut power to the system.

Step 2

Mount the unit in an area away from hot engine components or extreme

heat, such as exhaust manifolds, and away from moving parts, such as fans,

belts, and linkages.

Step 3

WIRING PROCEDURE

Step 1

Connect the BLACK WIRE to engine or chassis ground. You can use the

supplied “U” shaped terminal and #6 x 1/4" sheet metal screws to make

this connection. If you are connecting the RPM Activated Switch to an

grounding location that the ignition uses. See Figures 2-4, pages 2-3.

Step 2

Connect the RED WIRE to a 12-volt power supply, such as the ignition

switch. You can use the same wire that provides power for your ignition

as long as a ballast resistor is not wired in series with it. NOTE: Do NOT

connect the RED WIRE to the coil (+) terminal. Connect it to the

wire coming directly from the ignition switch. If your vehicle is

equipped with loom resistance wire, you must provide an alternate

power connection to the red wire.

Step 3

The GREEN WIRE must be connected to the ignition system tach output.

• When using a Mallory ignition system, connect the GREEN WIRE

to the TACH terminal. See Figures 2-4, pages 2 and 3.

• When using an aftermarket ignition with a TACH output, connect

the GREEN WIRE to the TACH terminal. Check manufacture’s ig-

nition instructions to find this location.

• Other aftermarket ignitions – Connect the GREEN WIRE to the ta-

chometer lead terminal. Check manufacturer’s ignition instructions

to find this location.

Step 4

To connect a device that you want to switch ON at the RPM setting

you’ve selected, such as a shift light, connect one ORANGE WIRE to the

device and the other ORANGE WIRE to a 12-volt power supply. Connect

the remaining wire from the device to a ground. See Figure 5, page 4.

Step 5

To connect a device that you want to switch OFF at the RPM setting you’ve

selected, such as a nitrous solenoid, connect one PURPLE WIRE to the

device and the other PURPLE WIRE to a 12-volt power supply. Connect

the remaining wire from the device to a ground.

Step 6

Secure all wires to prevent contact with extreme heat, sharp objects, or

moving devices, such as fans, belts, and linkages.

Step 7

Recheck all wires and connections to ensure that they are correct before

applying power.

Step 8

Reconnect the battery (–) terminal cable. Start engine and check operation

of the RPM Activated Switch.

Parts Included in this kit:

1 RPM Activated Switch Part No. 646

1 “U” shaped crimp-on wire terminal

1 #6 x 1/4" sheet metal screw

2 Velcro™ strips

General Information ...................................................................... 1

Mounting Procedure ..................................................................... 1

Wiring Procedure .......................................................................... 1

How to Set the Window RPM Switch ........................................... 2

Wiring Diagrams for the RPM Activated Switch

Connecting to a Timing Retard ................................................ 4

Connecting to a Timing Control ............................................... 4

Connecting to a Light ............................................................... 4

Connecting to an Electric (Shifter) Solenoid .......................... 5

Connecting to a Nitrous System .............................................. 6

Connecting to a Nitrous System and Timing Retard.............. 6

Shifnoid Warning....................................................................... 7

CONTENTS