Interior Rear Lights won't come on with switch

[slimak9]

W140
1993 300SD

When I hit the switch in overhead dome light unit to turn on the rear interior lights, only the 1 center light turns on. The 2 side reading lamps do not. These 2 side reading lamps do turn on though when the rear doors are opened or the button is pressed on them.

I know for a fact these 2 reading lights should turn on when the switch is flicked, as I saw it work in another W140. I even took the switch out from a working W140, but it did not fix it.

The only fuse I found for the rear lights was in the trunk.

Anyone have insight on whether a relay is the cause or know where the wires from the 2 readings lights conect to.