What year TIII is it? I know the '91's are the same as the T1 SBEC's. But, I honestly haven't looked ofr the shutoff code for the '92+. I'm not 100% sure it works the same way (IE, start and die). Maybe someone else can confirm.
If it is the alarm, I think wowzer has an update to MP Tune (not 100% sure he's set it to update yet) to wipe the EEPROM, which should clear the alarm bits and reset the computer. If you have a USB-SCI cable, you can try that.