You could always drown the switch in WD-40 in hopes that it's just a corroded contact. And while it's not so common, they do go bad internally, making it a booger to diagnose. You can go to the service manual schematic and test the switch by checking the continuity between the pins when the switch is engaged but that won't confirm the current carrying capability (and that may indeed be the culprit). With the switch on, grey should connect to brown, orange to red/white and red/yellow to green. The parking position connects brownn, orange, & red/white. I wouldn't rule out a poor contact at fuse 5 either.
