MSD 8501 Ultimate HEI Kit Installation - Manual (Page 3)

INSTALLATION INSTRUCTIONS 3
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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).
No Rev Limit: To disable the rev limit function, cut and remove the
jumper shown in Figure 6.
PROGRAMMING THE REV LIMIT
A tachometer is required to set the rev limit. The limit is programmed
by running the engine at half the desired rpm, then momentarily
grounding the Gray tach output wire from the MSD. A Gray jumper
wire is supplied to connect to the tach with another tee-splice coming
off to use for programming. A switch may also be installed to ease
adjustments of the limiter (Figure 7). The default rpm limit is 10,000
rpm. Note that the rpm limiter is extremely accurate and due to the
variety of tachometers available, there may be differences in the
displayed rpm.
1. Start the engine and bring the rpm to half the desired rev limit (for
a 6,000 rpm limit, raise the rpm to 3,000).
2. While holding the rpm steady, short the Gray tach wire to ground
for approximately one second. Note that the tach will go to zero
while grounded.
3. The tach will now display the programmed rev limit amount for
two seconds. If this value does not register on the tach, repeat
the procedure and try a different ground source.
Note: This rpm confirmation only displays when the HEI Gray wire
is being used to trigger the tachometer.
Figure 7 Setting the Rev Limiter
TO
TACH
OPTIONAL
PROGRAMMING
SWITCH
GRAY
Figure 5 Connecting the Module and Tach Lead.
TO ENGINE
GROUND
LONG BLACK
TO TACH
OUTPUT
GRAY
Figure 6 Disable the Rev Limit.
JUMPER