Can you read wire schematics?
Here ya go:
The black wire with a pink stripe provides the supply for the lamp, along with the interior lamp relay. However, the black with light blue stripe wire provides supply for the interior lamp. Based on the schematic above, if you tapped into the interior lamp circuit (BK/LB) with a toggle, you would be able to kill the interior (dome) light while maintaining the circuit to the Cargo lamp.