Vert owners please help!

I have a 00 v6 Vert mustang and my left rear window does not go down. I know the motor is fine because sometimes it will randomly work if I accidently hit my button to put it down. I was fiddling with it the other day and I was finally able to get the window to go up. All other window switches work fine. Is this a switch problem or wiring to the window problem? Any ideas on how to solve this problem or let my local dealer doit for me and charge me an arm and a leg?

Well the problem is I took my car to the dealership to fix the front left window because it needed to be fixed and the guy mentioned fixing that window to and I asked him how much and he said prolly couple hundred atleast because he said it would take "a few hours to diagnose the problem, then we still have to fix it" and my drivers side front window was 366$ so im scared to give the dealer it when I might be able to doit my self because it sounds like a loose wire or the switch. Because the motor is perfect and thats really the problems it could be, motor, switch or wiring. So im reluctant to have a dealer doit for me because diagnose at 90$ an hour plus repair = TOO MUCH. So ionno if I should just rip the door panel off and start checking wires lol.