I think most of the open source ECU projects are fairly young. I'm not too familiar with the Haltech so I can't answer about it specifically either.

I remembered reading about it on a Miata group from someone using it, which is why I went to go check it out for the CEL logic. I think there are probably other active ECU projects too though. I think Speeduino is another more well known one.

I know there are Miata guys running the project I mentioned. They list as having rotary support but I don't know how advanced or safe it would be for a FD. Using context clues it looks like someone may have gotten it setup on a RX8.

Edit: I know there is a guy on here selling a bluetooth adapter for the PFC to monitor all the sensor values. I think it is geared only towards Android, but in theory there would be nothing stopping you from using something like that to trigger a relay. It just depends on how hands on you want to get. I've been far too lazy to dig much into the PFC's output myself.

 

That sounds legit. Do you know what his name is?

I actually work in Bluetooth software for a living, so reverse engineering his protocol and setting it up on a Raspberry Pi GPIO or something would be pretty easy. The hard part is finding hardware that doesn't take a **** at 130F inside the car on a hot day lol. I did a project a few years ago for my 2004 Tacoma with one of those Chinese OBDII -> BT adapters connected to a Raspberry Pi Zero with a microdot display. It read water temp, RPM, I think speed, and some other things (I forgot) over BT from the OBDII adapter, and had a bunch of other sensors directly connected to its I2C bus (ambient temp, a CLOCK LOL, ambient light sensor to automatically dim its display at night...). It had some buttons for cycling the display, and a buzzer that would sound if the coolant temp got too high. It was really cool but never worked when you got into the car in summer until 5 minutes later after it cooled off. It also just never seemed to belong because it was fragile (and velcro'd onto the dash lol). Here's the BT adapter:
I would 100% like to play with something similar for the PFC.






Anyway, you were right, GND does the trick on the CEL! Mystery solved. It's connected and working exactly as I wanted!


Now I can get rid of the extra relay that inverted the AEM's fault GND output (on the right). Please disregard the flux and burn marks lol









It looks nasty, but it's actually not very invasive to any of the existing wiring in the car. Obviously the CEL is tee'd, and there are a few extra console switches. I stole the ACC power signal from the stereo adapter harness, and IGN from that spade slot on the interior fuse box. Other than that everything is pretty well left intact.

 

Oh cool. Yeah the output from the PFC is just serial with its own commands. I think they are mostly unofficially documented at this point though. So assuming you can listen to the serial connection like the handheld commander does, you could just set a bluetooth adapter to read/request stuff from the bus and then relay the results to whatever. I think his hardware module already does that, but the only client he had at the time was for android. Most likely you could listen to it using anything as long as you don't mind writing something to talk to his adapter and interpret the results.

I tossed together a head unit type thing to sit in the navigation hood for my RX8, but that was more just clever retrofitting and cobbling a lot of niche off the shelf products together into something (mostly) functional. It hasn't been subjected to the summer yet, but I think it'll do fine since it doesn't have any batteries or anything. At most the screen might wear out but that's easy to replace and I can always get a heat rated one on the next go around. This was kind of a ****-around-since-I'm-always-home project with whatever I had laying around the house.

Glad to hear that did the trick on the CEL. I am not sure why that didn't cross my mind originally so sorry about that. There isn't a whole lot the ECU actually sends +12v to so there's no reason for something like the CEL to be different. As much as I have had to screw around with my ECU harness you'd think I'd have thought about that sooner.

Yeah that's a whole lot of custom wires under the driver's side, but it looks like they are labeled and tucked away pretty good. Looks good, better than any custom wiring any car I have bought ever comes with. There are generic multi-pin connectors (like what your OEM harness uses) that you can get pretty cheap online. Once you are happy with the wiring you could replace all those 1-1 spade connectors with one of those so its a little less cluttered (unless there is a good reason you want to be able to disconnect only one wire at a time)

This is one of those things on my eventually list, with the big fluid tank in the oem trunk location. I did so much work on my 7 the last couple of years I am letting it take a break for a bit though until I can actually get some miles on it as-is and break all the new stuff (literally everything) in.