There is only one relay. The general test for a relay is to see if the output is as expected with the proper inputs. From your story, I'm guessing that the output you seek is domelights when the driver's door is openned.

Unfortunately, while the relay is a posible problem, it is not the relays function to operate the dome light. The circuit just passes through the relay.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician