inductive ignition system is just too noisy or inconsistent, a different RPM signal source will be
needed. A poor RPM signal can cause the RPM display on the Live Data screen to appear
erratic. It can also lead to inconsistent shift points under heavy load.
RPM Module Installation Notes:
• HEI distributors (and possibly others) have a terminal labeled “TACH”. However, that is not a
clean, processed tach signal like an aftermarket ignition box would supply. Instead, it is simply
another terminal connected to the negative side of the coil. Do NOT
connect the TACH IN / RPM
MODULE wire in the EZ-TCU™ wiring harness directly to that terminal. The TCU will be
damaged. In a case like that, the RPM Module is required since what you are really doing is
connecting to the negative side of a dwell controlled coil.
• Do NOT bypass the RPM Module and connect the TACH IN / RPM MODULE wire in the EZ-
TCU™ wiring harness directly to the negative side of the coil. It may actually work that way for a
time. But the TCU will be damaged and system performance will degrade.
• Do NOT connect anything from the EZ-TCU™ system to the coil – RPM Module or TACH IN /
RPM MODULE wire – when using an aftermarket ignition box.
• Use resistor type spark plugs. Non-resistor plugs are very noisy and interfere with electronics –
including the EZ-TCU™ system.
• Do NOT use solid core spark plug wires. These are also very noisy.
Speedometer Control Unit (SCU) (Not included in EZ-TCU™ kit)
An optional TCI® SCU uses an electric motor to spin a special speedometer cable to drive a
mechanical speedometer. The SCU wiring mates directly to the EZ-TCU™ wiring harness.
To configure the SCU for use with the EZ-TCU™, remove the SCU’s lid to access a row of DIP
switches. Set switches 4, 5 and 8 to the “ON” position. All others should be “OFF”. Once the
switches are set, the lid can be replaced. In the Setup Wizard or in the Advanced Options menu, set
the SPEEDO PPM to “4000PPM OR SCU”.
In other applications, the SCU needs the DIP switches to be set according to a formula based on
various drive train information. That calculation is not required for use with the EZ-TCU™. Once the
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