(OP of CaRFID here)
First thing is, I assume by xEM on the diagram you mean the xAC. Also, this reply might come off a bit negative, but know that I’m just giving feedback, and I wish you and your project the best
One thing I would note is this: I’m not sure to be honest if the relay on the xAC is SPDT or not. If it doesn’t connect to ground (aka if it’s SPST), I would ensure that you have pull-down resistors on your relay coil inputs, to ensure the input isn’t just floating.
Next, are you certain that your vehicle has both ACC and RUN enabled while the vehicle is running? I ask because on mine, ACC is not enabled at all once the key is past the ACC position in the ignition switch, and if your vehicle is the same, having both ACC and RUN connected could cause issues.
On a similar note, most cars also have a “key inserted” line that I would make sure is taken care of. Again, this is vehicle specific, but it’s something you’ll want to check. For my vehicle, if I was using a solution like this, I might replace the ACC position on the DPDT with the key insert position, as it can be triggered at the same time as the run position.
The biggest thing I wanted to address is the way you’re handling your relays. You’ve connected your start relay to an LTC6993, I’m assuming that’s to handle your start timing? One thing to keep in mind, the xAC does not latch it’s relays, you cannot use it to directly run your run/acc relay in your example. However, you can configure the timing to I believe 1 or 3 seconds using a jumper on the board. So, what I would do, is hook the xAC output to your start relay, and configure it for 3 seconds. That should be enough to crank the engine over.
Then, to handle the run/acc relay, I would probably use a simple flip-flop, with the set pin hooked to the xAC output, and the reset pin hooked to a button that would act as your stop button, connecting to 5V/3.3V.
I would also add a master cutoff switch, as the xAC draws considerable power enough to where I wouldn’t leave it on constantly.