I’d start looking at a wiring diagram and see what ground circuits are in that smaller ground cable. So you removed the starter with the battery still connected? Car running or not, there’s power if you didn’t disconnect the ground wire when pulling the transmission. Always pull the negative battery terminal before disconnecting anything. I would get Alfa obd it’s free to use (for a short amount of time), but you need the obdii dongle. My fuel light would blink and I’d get a message (service fuel sensor) but no codes. Scanned with Alfa and it told me there was a BCM code stored for a short to ground on fuel level sensor B, which was great because it told me which floater went bad (the cars have 2). You replaced everything I would have looked at as the first culprits (battery, alternator, ground strap.) you checked your intelligent battery sensor? It’s the connector on the negative battery terminal