About
The purpose of the GM ECM Harness Adapter board (Fig. 1) is to allow the installation of
a 1227747 or 1228746 ECM into a Cross-Fire Injection equipped Corvette, Camaro, or Firebird
without the need for extensive modifying of the original wiring harness in the car.
The Cross-Fire equipped cars came from the factory with an ECM that uses edge-card type connectors (Fig. 2) for the wiring harness.
Vehicles equipped with an 1227747 or 1228746 ECM use a pin-and-socket type of connector (Fig. 3)for the wiring harness.
By removing the original pin-and-socket connector from the ECM main board and replacing it with the Harness Adapter Module, the ECM can connect directly to the original wiring harness in the car without the need for any wire cutting or splicing, or the need for any "pigtail" adapters. See "installation"
Options
The Harness Adaper Module comes with a few options for the user to consider.
These options may be selected with the ordering form.
1228746 IAT sensor:
If the Module is to be used with a 1228746 ECM, then an Intake Air
Temperature Sensor (IAT) will need to be installed. There are two options
available for getting the signal from the IAT sensor to the ECM:
1) An extra dedicated wire may be added to an unused pin on the ECM
connectors (Black pin 21), routed through the firewall grommet, and
connected to the IAT sensor. If so requested a connector terminal with a
few inches of wire will be provided with the Module. The user must insert
the terminal into the black ECM connector pin 21 and splice a length of 18
gauge wire (not provided) long enough to route through the firewall grommet
into the engine compartment to the user-installed IAT sensor. The ONLY
acceptable method for splicing these wires together is with solder and heat
shrink tubing!
2) If the AIR switch is not being used, then the IAT sensor signal may be
connected to the AIR SWITCH wire (Black pin 14).
Support for WINALDL:
1) The voltage level translator circuit required for WINALDL is built in to
the Harness Adapter Module. The converted signal may be routed directly to
the ALDL connector, allowing a direct connection between the ALDL connector
and a PC serial port via a user-provided cable. Note: in this configuration
the ALDL port will NOT function correctly with any other type of scanner.
This configuration will not affect the ability to retrieve codes by
connecting pins A and B of the ALDL connector.
2) A DB9 connector may be provided for making the connection to a PC serial
port for WINALDL, leaving the ALDL serial data in it's original form for use
with GM or aftermarket scanners. The user will need to use a DB9 direct
connection (NOT a null-modem) extension cable (not provided) to connect the
ECM to a PC serial port.
Hood induction louvre driver:
For 1982 Corvettes and for Camaros/Firebirds, a driver circuit may be
included to control the louvre relay. The driver circuit monitors the TPS
voltage and energizes the louvre relay at approximately 3/4 of
full-throttle.
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