88 Mustang won’t start?

New to this site, finding a lot of great information. Been having an idle issue with the mustang so was going about testing the voltage at the TPS sensor and by accident instead of checking current at the negative wire I accidentally sent power to it (using a power probe). As soon as it happened I heard a popping noise and now the stang won’t start. When cold I can get it to start if I press the accelerator pedal down a little and the TPS is disconnected. Once running the car runs ok until it warms up then if I shut it off it won’t start till cool. I tried to run KOEO codes with my scanner but it won’t go into self diagnostic mode. It looks like I damaged the SigRtn (46) wire. Hopefully I didn’t hurt the ECU. Any help to get this fixed and running would be greatly appreciated.
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Kinda sound like you cooked the ground trace in the computer, pull it out and open it up and look
So I get home today had to put the top up on it and decided to try to start it and it starts right up. Was running a little rough but was just happy to just have it start with just the turning of the key. I am off Thursday so I will look into it more. To me if I fried the ECU it shouldn’t have started.