S&S Cycle IST Ignition System for 1984–99 4 1/8 Bore Big Twin Engines User Manual

Page 3

Ignition Coil Identification

Dual Fire Coil

In addition to the spark plug terminals, an aftermarket dual fire coil will have two wiring terminals: positive, negative.

Single Fire Coil

In addition to the spark plug terminals, an aftermarket single fire coil will have three wiring terminals: A negative terminal for the front cylinder,
a common 12v + terminal, and negative terminal for the rear cylinder, this is the most common type of single fire coil.

All single fire coils are compatible with the S&S ignition if they have a resistance of 0.5 to 3 ohms. The standard rating for an aftermarket single
fire coil is 3 ohms. Coils with higher resistance will decrease ignition output.

The S&S® Ignition system will also support a variety of different ignition coil combinations as long as they are connected for single fire operation,
and yield a final resistance of 0.5 to 3 ohms.

Spark Plugs and Plug Wires

Spark plugs must be resistor spark plugs (suppression type) of the correct style and heat range for the application. Do not use non-resistor
plugs

Spark plug wires must be suppression type. Do not use solid metal core plug wires.

B. Parts List
The S&S IST Ignition Installation Kit for S&S 41⁄8" bore engines
(S&S 55-1050 See Picture 1, below left) is intended only for installation of S&S Intelligent Spark Technology (IST) Ignition Module (See Picture 2,
below right).

All reference to Harley-Davidson® part numbers is for identification purposes only. We in no way are implying that any of S&S® Cycle’s products are original
equipment parts or that they are equivalent to the corresponding Harley-Davidson® part number shown.

Picture 2

S&S® Intelligent Spark Technology Module

Picture 1

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