My instrument lights are permanently dim on my 1993 Volvo 240. I replaced the dimmer rheostat with a donor, and after the swap the headlight stay on after the key is removed from the ignition switch. If I unplug the wires to the back of the dimmer rheostat, I hear a relay click (perhaps behind the instrument panel or radio?) and the headlights go out. Reconnecting the dimmer rheostat does not cause the headlights to go on.

So, I used a double spade to connect to bypass the dimmer rheostat, and connect the wires to eliminate the dimmer rheostat. Same result: headlight stay on, remove the spade connecting the double red/white and double brown wires (see attached image) and relay "clicks" and the headlight go out. So, it's not the dimmer, because even when it is eliminated the problem exists. I can simply not connect the rheostat wires and tape off the terminals, but then I'll have no instrument cluster illumination of any kind.

What are the possibilities? Sticky relay? Bad headlight switch? Bad ignition switch? What possible electrical faults would cause the headlights to stay on when the key is removed?

Is there an alternative way to provide switched power to the instrument cluster lights when the ignition key is on?