I can't seem to remove the instrument. It's mounted on a bulkhead next to the companionway. I can see the two thumb screws from inside, but when I remove them the instrument does not budge. Do I need to pull harder or am I missing something?
Yes, "pulling harder" would be the approach (carefully). There are only two screws at the top-right and lower-left (looking at the front) of the instrument holding it in. Anything else holding it in is probably sealant (pray it isn't 5200). Before I bought my boat, someone stole several of the PO's instruments by simply prying them off the panel without even removing the screws. Some of the studs remained behind along with the threaded bushing that was formerly part of the instrument.
Next question: I don't believe my instruments are networked. If I try to display apparent wind I get ---. Is networking the ST 60 Speed and Wind as simply as plugging in a Seatalk cable?
Yes again, if the Speed and Wind instruments are on Seatalk they will share data and calculate true wind, VMG (to windward), etc.
Mind you, you should be seeing Apparent wind already - that's the only thing the Wind instrument measures. It uses STW (boatspeed through water) from Seatalk to calculate True wind speed and angle from Apparent. Not that the "True" and "App" flags on the display are all that evident.
If Apparent is ---, you don't have any windspeed info. If it shows you True wind but not Apparent, you may have the instruments networked via Seatalk after all, in which case the Wind instrument may be seeing boatspeed, and, thinking that Apparent Wind = 0, concluding that you are motoring dead downwind at exactly the windspeed, hence True Wind = Speed and Wind Angle = 180.