According to the wiring diagrams for both the 2006 and 2007 Sightseer 26P, the switch should be on the opposite wall from the shower at the rear of the opening to the bathroom facing the shower. It should be a double switch with one switch labeled ˜Shower'. If this switch isn't working to turn on the lamp in the shower, then check the bulb or see if a wire has come off the back of the switch. Be very careful removing these switches, they are made to be assembled quickly in the factory but don't come apart very easily at all. The plastic pins that hold the pieces together brake off. I have had to repair two such switches and managed to brake both. They will hang together with one pin broken. If you still can't get the light to work, then I would suspect a wiring problem like a pin popped out of a connector. Check the diagram for the 2006, it appears to be the same as the 2007 but is more complete then the 2007. Looks like only one connector between the switch and the lamp.
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