The neutral safety switch has nothing to do with the shift interlock system.
Customer Concern: Cannot shift out of the park position. The Center High Mounted Stop Light (CHMSL) is not working. The outer brake lights work if the ignition switch is on. Tests/Procedures: 1. Check if fuse #24 in the TIPM (Totally Intergrated Power Module) is good.
2. Check that the Tan/Red wire at the brake switch has power at all times. Load test this circuit using a spare headlight.
3. Check that there is B+ on the White/Tan wire at the brake switch when the brakes are applied. If not, the switch is bad.
4. The instrument cluster sends out B+ on the Orange/White wire to the BTSI solenoid when the brakes are released. The cluster gets voltage on the White/Tan wire when the brakes are applied and stops sending voltage to the BTSI to release the shifter. The White/Tan wire also goes to the CHMSL. Tech Tips: The outer brake lights get power from the TIPM. The TIPM gets a bussed message from the cluster when the brake pedal is applied. If the cluster does not get power on the White/Tan wire but the Powertrain Control Module (PCM) and Controller Antilock Brakes (CAB) get a signal that the brakes are applied, one of the modules sends a bussed message to the TIPM as a failsafe. This failsafe only works when the key is turned on.