MSD 83647 Installation

MSD HEAT Digital HEI Module

PN 83647

ONLINE PRODUCT REGISTRATION: Register your MSD product online and you’ll be entered in our
monthly 8.5mm Super Conductor Spark Plug Wire give-away! Registering your product will help if there
is ever a warranty issue with your product and helps the MSD R&D team create new products that you
ask for! Go to www.msdperformance.com/registration.

This Module is a performance replacement for GM’s 4-Pin HEI Module. It features a programmable
rev limiter for overrev protection. The Module will mount in a stock HEI housing (by removing the
original condenser assembly) or in MSD’s Pro-Billet HEI Distributor, PN 8365. A GM Coil can be used
or for maximum performance, use MSD’s HEI Coil, PN 8225.

Parts Included:

1 - HEI Module, PN 83647
1 - Tube of Heat Sink Compound

Note: A tachometer is required to program the rev limit.

INSTALLATION

1. Mark the location of the spark plug wires on the cap prior to removal.

2. Remove the cap, rotor, module and condenser (if equipped) from the original distributor.

3. Apply a liberal coat of the Heat Sink Compound to the aluminum base of the Module.

4. Route the wiring harness out of the housing and position the short Black wire to ground with one
of the mounting screws (Figure 1).

5. Position the module in the distributor then locate the two screws and star washers to secure the
module (Figure 1).

6. Reinstall the rotor
and cap.

REV LIMIT

BYPASS
JUMPER

1 - Gray Tach Wire
2 - Mounting Screws and Star Washers
1 - Low Resistance Rotor Bushing, PN 8412

SCREWS AND

STAR WASHERS

CONNECT SHORT

BLACK WIRE

TO GROUND

CONNECTOR

CAP

DIGITAL

HEI MODULE

APPLY

HEAT SINK

COMPOUND

DISTRIBUTOR

HOUSING

TO TACH

GRAY
TACH
OUTPUT

USE TO
PROGRAM TACH

Figure 1 Installing the Module.

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

7. Connect the HEI Module harness to the Distributor Cap followed by the 12 volt (BAT) wire. This
wire should be at least 14-gauge (Figure 2).

8. Connect the long black wire to the engine block for a solid ground.

9. See the next page for tachometer and rev limit programming.

10. It is recommended to install the supplied low resistance rotor bushing. This improves the spark
transfer from the coil to the rotor tip. Remove the coil cover and coil. Replace the rotor bushing.

GRAY

TO TACH

OUTPUT

LONG BLACK

TO ENGINE

GROUND

Figure 2 Connecting the Module and Tach Lead.

TACHOMETER INFORMATION

The HEAT Digital HEI Module has a Gray wire that provides a 12 volt
square wave, 20° tachometer signal that will trigger most tachometers.
It is recommended to connect this lead to your tach’s trigger input
wire and check its operation. If the tach requires a higher voltage
signal, connect its input wire to the Tach terminal on the HEI Cap
(Coil-/Tach). Note that the rpm limiter is extremely accurate and due
to the variety of tachometers available, there may be differences in
the displayed rpm.

No Rev Limit: To disable the rev limit function, cut and remove the
jumper shown in Figure 3.

JUMPER

Figure 3 Disable the Rev Limit.

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