The mirror will probably end up being the switch. I tinted cars for years, and they use a lot of soapy water to keep the film free to float on the glass until they have it where they want. Once its there they squeegee all that water out and it has to go somewhere. Most of the time it goes in the door and evaporates over time. I would take apart the switch, get some contact cleaner (its safe for electronics), spray it in there, let it sit for a couple days and try again. The residue from the soap may be making the contacts intermittent. Hope that helps...

to werkz btw...