how to diag for no interior lights

Check and make sure that the dimmer switch isn't turned down all the way causing no power to the dome lamps. If thats not the problem check the bulb and make sure its not blown then check for power to the socket the bulb goes in. If none of that is the cause you could flip a coin or post the results and someone will be happy to direct you to a more involved diagnosis.

Just read your other post, the interior lamps relay is in the aux relay box #2 that is located behind the instrument panel. If you are flexible you can see it from the drivers footwell. Look up while laying on your back like a contortionist its above the gas pedal. It should have black tape wrapped around it that has to be removed before the cover will come off. You are looking for a rectangular box about 4 in long and 2 in square. the relay itself is one of the smaller ones. While looking at it with the cover off there will be one large relay at the bottom and 2 rows of 3 above it. You want the second small relay up on the left from the bottom. It ain't fun to get to but can be done. War Eagle!