PRNDL & Odometer Displays Do Not Illuminate When Ignition Is On, Unless TRIPMETER Switch Is Pressed.

An open or short to ground in circuit 1020 (Pink wire) will result in displays not illuminating. IPC will not communicate with scan tool. If tripmeter switch is pressed, display will illuminate and IPC will communicate with scan tool while switch is pressed.

Check IPC power and ground supply. See IPC POWER & GROUND CHECK  under COMPONENT TESTING. If power and ground supply are okay, replace IPC.