Stop Light Switch Circuit Test

Turn ignition on and check stop fuse. If not normal, there is short in harness between terminal 8 or 9 (Celica, Cressida, Supra and Corolla) of computer and fuse. For Pickup and 4Runner, applicable terminals are 11 or 12. For Van, check terminal 12.
If fuse is normal, check computer. Disconnect computer and inspect connector on wire harness side as follows: For Van, go to steps 5) and 6). For all others, depress brake pedal and inspect release valve circuit by testing for continuity between terminal 1 and 2 (Celica, Supra, Cressida, and Corolla) or 2 and 17 (Pickup & 4Runner). If there is continuity, inspect stop light switch.
If no continuity existed in step 2), inspect stop fuse circuit by checking for 12 volts between terminal 9 (Celica, Cressida, Supra and Corolla) or 12 (Pickup & 4Runner) and body ground. If not okay, check for open in harness between terminal 9 or 12 (as applicable) and Stop fuse.
If continuity existed in step 3), depress brake pedal and check for 12 volts between terminal 8 (Celica, Cressida, Supra and Corolla) or 11 (Pickup & 4Runner) and ground. If continuity, replace computer. If none, check for open or short between terminal 8 of computer and 2 of stop light switch (Celica, Cressida, Supra and Corolla) or 11 and 4 (Pickup & 4Runner).
For Van, depress brake pedal and inspect actuator circuit by disconnecting computer connector and testing for continuity between terminal 5 on harness side and ground. If no continuity, inspect brake cancel switch. If there is continuity, check Stop fuse circuit by checking for 12 volts between terminal 12 and ground. If none, check for open in harness between terminal 12 of computer and Stop fuse.
If continuity existed in step 5), inspect stop light switch circuit by depressing brake pedal and checking for 12 volts between terminal 11 and ground. If yes, replace computer. If no, there is open or short in harness between terminal 11 of computer and 2 of stop light switch.