How to get students to connect the pre-lab to the lab?
Don't do the pre-lab. 

Divide the lab experience in two or more sessions, where they have to do the calculations first and the measurements soon thereafter.

And avoid online quiz with feedback: the answer is plausible if it's compatible with the measurements, not because the computer says so.

For long calculations, I sometimes use an intermediate solution in which they have to perform the calculations as homework, but they read what they have to do in the lab instruction manual, so that the two things appear connected. For example:



In this way, they are forced to read the whole lab manual first. And of course I tell them and write them that the calculations are part of the lab.