INSTALLATION INSTRUCTIONS
M S D I G N I T I O N
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oPtIoNAL WIRING
This Wiring Section details the optional features of the MSD 7AL-3 and how to wire each system.
StARt RetARD
The Start Retard of the 7AL-3 is designed to ease starting on engines with locked timing, high
compression and a lot of advance. When activated, the timing is retarded 25°. Some engine
combinations benefit from this retard, while others may experience rough starting or starter kickback.
If your engine experiences roughness with the start retard engaged, the retard is not necessary.
When activated, the Start Retard function will retard the ignition timing 25° while the engine is cranking
which makes starting easier as well as saves wear and tear on the engine and the starter. This retard
function will only operate below approximately 1,300 rpm. There are two different ways to connect
this function (Figure 7):
a. Switched 12 Volts
In this set up, the timing is retarded 25° only while the engine is cranking. Connect the supplied Violet
wire from the “Start-Ret” terminal on the 7AL-3 to the starter solenoid. This way, 12 volts is only applied
when the key or switch is in the cranking position. When the switch is released, 12 volts is removed
and the timing returns to run timing.
B. Constant 12 Volts
In this setup, whenever the ignition is turned On, 12 volts is applied and the retard function is activated.
The retard will be deactivated when the engine reaches about 1,300 rpm and will not occur again
until the ignition is turned
Off
. Connect the supplied jumper from the Start-Ret terminal to the Ignition
terminal of the terminal strip (two terminals up).
tHRee SteP RPM lIMItS
The 7AL-3 has a built-in Three Step Module Selector which allows you to select up to three different
rpm limits that occur at different times. The activation terminals are located on the bottom of the
third terminal strip and are listed as Launch and burnout. The third rpm limit is the high rpm, which
is always active when there is an rpm module installed in the "Race" holder (except when the other
rpm limits are activated).
These modules can be used in a variety of functions and are not limited to launches and burnouts.
Each of the two optional rpm limits are activated when 12 volts is applied to their corresponding
terminals (Figure 8). The 12 volts can come from switches, solenoids or relays giving you a variety of
ways to activate the different rpm limits. The following steps illustrate a general drag race installation
for use with a burnout limit, Launch limit and Race limit.
Figure 7 Wiring the Start Retard Function.
