RX-7 86-88 (S4) Factory Harness to Megasquirt MS2 Adapter


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A direct plug-and-play adapter harness that allows you to use your existing factory wiring harness with a Megasquirt MS2 assembled/modified for an 86-88 Mazda RX-7.

This harness is made to work with your Megasquirt assembled/modified as outlined in Aaroncake’s how-to (link here). (CAS on pins 2, 3, 4, and 24. Trailing coil trigger on pin 27, trailing coil toggle on pin 29,and leading coil trigger on pin 31.)

EXCEPT to prevent damage to the Megasquirt, we have left the BAC (Bypass Air Control) idle valve’s ground unconnected. If you will be controlling a BAC valve with Megasquirt, follow all modification instructions outlined by Aaroncake, then connect factory ECU pin 2Q to Megasquirt pin 30. Be sure to install the required diode to prevent inductive kickback to the drive transistor, as well.

The factory oxygen sensor from original ECU pin 2D comes connected to pin 23 for the Megasquirt’s oxygen sensor input. If you are running a wideband, you will need to desolder and remove the wire from pin 23 to ECU pin 2D completely, then solder your 0-5V wideband output into the solder cup for pin 23. For the most accurate reading, you will also need to ground the wideband to the same source as the Megasquirt. See the following link for more information: Megasquirt Grounding

You will need to rewire your fuel pump relay, as the factory setup depends on the switch inside the Mass Air Flow sensor to activate the relay. We recommend using a relay with a fused feed from the battery to the fuel pump (across relay pins 30 and 87), switched by pin 37 of the Megasquirt as ground (relay pin 85), and a switched ignition +12V source on pin 86.

Additional information

Weight 0.8125 lbs
Dimensions 7 × 7 × 7 in