Instruments Lights Not Dimming

[mikee boy]

My interior instrument dimmer switch (S2 rotary) doesn't work in the centre (dimmed) position. The switch is fine and I've worked out it's the resistor or the wiring to/from the resistor but I can't find where this resistor is as the wires to/from just disappear into the wiring loom. Any ideas or should I just make another in which case what's the resistance I'm after?