Speedometer pickup on 1993 Force 150?

I recently obtained a 1993 Glastron SSV 190 equipped with a Force 150 outboard. The motor runs great, but the speedometer is not working. I'm guessing the speedometer input hole is plugged....however I can't tell where that hole is on the Force 150. I see where the black tube enters the lower unit, but its not obvious (to me) where the water enters the system. I've searched around a bit on the internet but can't find a diagram. Can someone tell me were that intake is? Do I have to remove a cover or something to access and check to see if it's plugged?