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Definitely sounds like a wiring issue. An easy place to start checking is the fuses, but that's probably not likely since it is both the lights and the trunk switch.
The car will set diagnostic trouble codes if the lights aren't working, but you would need a GM Tech 2 scanner to see those. I would start by checking the connectors.
When the lights are turned on, a ground signal is sent from the light switch to the park lamp circuit in the body control module. The BCM responds by supplying voltage to the lamps.
Pin 6 on the body control module X4 connector is the left park lamp supply voltage.
That wire goes to pin 13 on the X900 connector, and then pin A on the left park lamp connector (the x900 connector is located on the drivers side wall of the trunk).
I would check for continuity between all of those. If there is continuity, then you might have a BCM problem.
The car will set diagnostic trouble codes if the lights aren't working, but you would need a GM Tech 2 scanner to see those. I would start by checking the connectors.
When the lights are turned on, a ground signal is sent from the light switch to the park lamp circuit in the body control module. The BCM responds by supplying voltage to the lamps.
Pin 6 on the body control module X4 connector is the left park lamp supply voltage.
That wire goes to pin 13 on the X900 connector, and then pin A on the left park lamp connector (the x900 connector is located on the drivers side wall of the trunk).
I would check for continuity between all of those. If there is continuity, then you might have a BCM problem.