Database design for a car dealers website
I would say that your second suggestion, haivng a TechSpecID in the Vehicles table, makes the most sense. A way of thinking could be, is a Vehicle implementing a TechSpec or is a TechSpec implementing a Vehicle? I.e. what comes first (the Technical Specification) and what is 'using' your Technical Specifications (the vehicles). But, in the end, it's all down to your context and what makes the most sense in your particular situation.

You have a very broad question so it is difficult to answer specifically what you might be looking for.

One thing I'd like to point out, however, is that most people don't prepend tg_ or fwk_ to their table names. You could use schemas if you'd like to differentiate them some...