Slowmiatadude

Okay to sum up the story. I built a diypnp 2 extra 1.5b revision board for my 1995 miata. It was running great and I had tuned the idle in the shop. My afr guage wasnt reading when plugged into the output and input port on the megasquirt I believe it's called the db15. Might be wrong. I'm a complete beginner at electronics and this was my first project with circuitry. I decided to test the outputs I had wired into the megasquirt which were a 12v out ground and the afr guage in. I thought I had them mixed up so I took a voltmeter and tested the 12v out pin by grounding the ground electrode to the car and touching the 12v out from the computer. ZAP smoke came out of the ecu. I tried starting the car but it ran around 8 to 9 afr. I had it previously running around 14.3 or so. So I hopped on tuner studio to confirm nothing had changed and reburned my tune to the megasquirt. Same thing. I then started subtracting fuel from my ve table until the numbers were at 1. It ran around 11.6 afr and when on 0 you guessed it. It doesnt run. I took the ecu out of the case and took the top card off to inspect for burn marks. the ECU looks perfect. I plugged it back in and tested the injectors and coils on the test mode it all checked out and was operational. I even took a timing light and put it on all the separate wires to make sure it was firing on all 4. So did I just pay 500 hundred bucks to here a car idle for 3 days or is there a way to check and diagnose the circuitry on my own.