I previously covered several connections between the Honda Harness and the car via an 8 pin connector I added in the engine bay, but that is only half the connections. Here is what is wasn’t included in that:
-Fuel pump relay
-Engine speed pulse
-Starter switch signal
-Oil pressure sender
-MIATA TEMP SENSOR
-Wide band #1 signal
-Wide band #2 signal
Each of these connections take place in the cabin of the car, or are independent of the Honda harness. This entry will cover the first 3 that have been completed, along with the plans for the others. NOTE- Several of these connections are via the ECU’s A Plug. The A Plug did not come with the harness, as it is part of the dash harness on the Acura. I previously posted about purchasing one new.
Fuel Pump Relay- The AEM is set up with a pin on the A Plug that goes to ground to trigger a fuel pump relay. For the 1.6 Miata, there is a LT GRN wire at the fuel pump relay under that triggers the relay when it goes to ground. It typically finds it’s way to ground via the AFM or the diagnostic port. I tapped in to this wire with a new green wire and ran it over near the ECU (more on this in a minute). I chose to tap instead of replace because I wanted to maintain the ability to trigger the pump via the diagnostic port.
Engine speed pulse- The AEM has an output for engine speed pulse on the A Plug. I’m hoping that I will be able to adjust that signal in the AEM to allow it to properly drive the Miata Tach, but I will figure that out later. To get the signal to the tach, you don’t actually need to get near the instrument cluster. It’s signal comes in to the dash harness via a YEL/BLU wire at the a plug under the passenger side of the dash to the right of the glove box. I was able to remove the pin from the car side of the plug. I actually had a YEL/BLU wire with pin on it that had been removed from the Honda harness that I was able to snap right in to the Miata plug. By going this way, I am able to connect to the tach without adding a new connector between the dash and car. That will be useful when the dash is removed in the future.
Here you can see the connector referenced, with the old YEL/BLU wire taped off and the new one in place.
For connecting the Fuel pump and tach wires discussed above to the the A Plug, I wanted to have the ability to disconnect them. Below is the plug I used. On the left, you can see the GRN and YEL/BLU wires coming it, and the right side they are run to the A Plug.
NOTE- I bought a bag full of these plugs online, I am not happy with them, and will probably replace them eventually, but they will do for now.
Starter switch signal- The AEM needs to get a starter switch signal through the A Plug. For the 1.6 Miata, I found that the violet wire at 1C of the Miata ECU can cover this.
A/C- For the 1.6 Miata, you can bypass the ECU by connecting the wires at 1Q (LT GRN/BLK) and 1J (BLU/BLK). I have done this, but I also eventually want the ECU to know when AC is on so it can adjust idle. The AEM has an A/C Input pin on the A Plug, but I don’t yet fully understand how it works and if I can simply connect it to where 1Q and 1J are connected. Just in case it is that easy, I have taped off wires right next to each other and ready for a butt connector.
Below you can see another 2 pin connector in use. The violet wire for the starter switch signal goes to the A plug through here, and you can also see the taped off A/C wires that come through it.
The ones left to do:
Oil pressure sender- This will be simple once the Miata Oil Pressure sender is installed on the V6. I will just need to run a single wire from the sender and connect it to the YEL/RED wire that was originally used in the Miata harness to carry this signal to the instrument cluster. This connection will be done in the engine bay.
MIATA TEMP SENSOR- Another simple one. I will run a single wire from the the sensor to BLK/BLU wire in the Mazda harness that originally carried this signal to the instrument cluster. Again, this connection will be done in the engine bay.
Wide band #1 signal- This is an input via the A Plug. I ran a wire/pin into the A Plug for it, so I am ready when I install the Wide band.
Wide band #2 signal- The AEM has a pin ready for a second wide band. I don’t know if I will run 2 for use, but it would improve tuning if I had one off each header. I ran a wire/pin into the A Plug for it, so I am ready If I install a second one.