Hello George, the interior lights are switched by 4 contacts that activate the XIX relay (1990 model). Thinking the lights stay on since some spray work was done and it was ok before, I'd say it is likely a contact issue and not the relay itself. Pull relay XIX and check on the CEB pin L12 what you measure. If it is 0 ohm against chassis you have an active contact causing this. If it is infinite the contacts are open and this is not causing the interior lights to stay on. The relay is suspect.

The door contact left and right is relatively simple. You can take them out to verify that the wire is still connected. If you find one with the wire off, the wire may touch chassis which causes the lights to stay on.
On contact goes to the power window / sunroof controller pin 5.
And there is a connection to the timing relay is you have that. (M215/M553, not for RoW)

And then there is the hatch contact. This activates the lights directly without using the XIX relay. So if you hear XIX relay click after opening and closing the door and the interior lights all stay on, your focus shifts to the hatch contact. closing of the hatch immediately turns off the lights where closing the doors uses the delay via XIX. Knowing this helps diagnosing.

Oh, just for noobs: all lights can be switched on manually on the light assembly. If all are switched on obviously they stay on.

1992 928GTS midnight blue
The Netherlands