I have a similar issue with a 2004 Sequoia SR5... Pulling the 7.5A fuse does nothing... Also, I cut the black STSW wire (E6 #12) at 1.5" from the ECU. The result is the same: turning on the ignition causes the starter to crank. TIS shows "starter sig" on. Turning ignition off does not stop starter. Only removing starter relay, but EFI, C/OPN, Fuel Pump relays still click. Disconnecting battery stops cranks and clicks...
Another ECU behaves the same way... Turning the ignition on turns the starter.
Your question has been split off into its own topic. For future reference, please don't "hijack" someone else's old post when asking about a car problem. Thank you.
You didn't mention anything about testing the ignition switch itself. Has this been done?
I would replace the ignition switch
I did it. The STA signal turns on and off as expected... Furthermore, I not only tried pulling the 7.5A fuse, but also physically cut the STSW wire on the ECU...
BTW, ECU # 89661-0C550