Technical information

AUTOTRONIC CONTROLS CORPORATION • 1490 HENRY BRENNAN, EL PASO, TEXAS 79936 • [phone] • FAX [phone]
www.msdignition.com email: [e-mail]
121
TACHOMETER INFORMATION
Note #3 GM Inline Filters
Many General Motors Corporation vehicles have an
in-line filter that should be bypassed when the factory
tachometer drops back to zero as the engine RPM is
increasing.
The drawings at the right show what the filter might
look like. Locate the filter by tracing the wire from the
TACH Terminal on vehicles equipped with an HEI Ignition
System.
On vehicles equipped without an HEI, trace the wire
from the coil negative terminal until the filter is found.
Disconnect both wires from the filter and leave dis-
connected. Connect the wire going to the tachometer to
the MSD Ignition Unit Tach Output Terminal as shown in
this Figure.
Note #4 Current Triggered
If the tachometer is connected to the positive side of
the ignition coil, do not attempt to connect this tachom-
eter to the tach output terminal on the MSD Unit.
See Note #1 for a diagram of an original current trig-
gered tach. The tachometer is connected to the positive
side of the ignition coil. The ballast resistor or resistance
wire can be on either side of the coil.
The diagram to the right shows a Chrysler Dual Ballast
Resistor being used with a WHITE Wire Triggered installa-
tion. The Chrysler Dual Ballast Resistor is from a 1973 to
1976 Chrysler electronic ignition system and may be pur-
chased from any auto parts store. The additional resis-
tance may correct the tachometer function.
TACH ADAPTERS
AUTOTRONIC CONTROLS CORPORATION
1490 Henry Brennan Dr., El Paso, TX 79936
PN 8920
TACH
ADAPTER
PN 8910
PN 8910EIS
PN 8920
PN 8912