wipers won't work in 3rd (very fast) position
 

My wiper switch on my 87 carrera doesn't seem to work in the 3rd (very fast) position. It works fine in the 1st and 2nd positions. In the 3rd position, the wipers stop where they are on the windshield when that position of the switch is activated.

Ideas on where to start troubleshooting?

I suspect the contact on the wiper switch is corroded or not making proper contact. You will have to remove the switch to fix it. Not sure it is worth the trouble as the 3rd speed is so fast that I have never used it even in a heavy downpour!