Hi there, Yep, it's the dimmer control, should be a slider beside the light control switch beside the door. Try turning it up to full brightness and they should come back on as they've just gone very dim. If not then the variable control may be damaged and forcing it all to low brightness.
It might not be as easy as that. First port of call, check the RDO/IP IGN fuse as shown in the attached as cripsinchurch as hopefully that's all it is.
Next one to check would be the movable fuse marked 12V OUT IGN OR BATT, as some installers may choose this if they've bypassed the wiring harness to get around the amplifier or other components (and spliced into the power loom going down to the 12v lighter socket).
