I'm not familiar with the 68's but on my 66 you just have to pull out on the wiper switch. Pull on it gently and listen for a little electric motor. If you hear it then you probably just need to make sure all the lines are connected and fill the tank. If the knob pulls out but you don't hear anything than it's probably disconnected. Then again the 68's could be completely different than the 66's. It's worth a shot though.
Brett
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66 Tahoe Turquoise Coupe
Laser Red 96GT Ragtop
30 Years & 30 inches apart in the driveway!