Battery off, switch on, check ohms between battery + lead and earth for starters, should not be 0 ohms
If ok .....
Leave the TCI box disconnected and connect battery and watch for smoke but put smaller rated fuses to start with see if all the basic electrics (blinkers etc) work.
Then replace correct fuses and try the starter motor if that spins ok switch off reconnect TCI and regulator.
Fuel up
Press starter.
My 2 cents worth