Hyundai Elantra 2006 2.? 249000 miles
Battery light came on, went off parked it. Get in the next day and radio wasn't working. Drove it, got out went to leave, radio worked, low beams went out. Went to troubleshoot the low beams, heard a hissing from the battery, put new one in, didn't start, had the alternator checked, bad, so replaced it, still no start. Took the starter in to get checked. It passed. So I waa thinking it's a loose wire or a bad ground or something. Or the ecu. Took the ecu out and it looked good, (no obvious burn marks. Haven't found any loose connections or bad grounds. Not sure what to do next, I wanna try everything before I send in the ecu, it's expensive. I'd hate to send it in and pay, and there not be anything wrong with it. Any ideas moving forward??