Further to my previous question, 
http://electronics.stackexchange.com/questions/47247/using-a-pic-to-perform-switch-on-and-timed-shutdowns-in-automotive-environment

I've been pointed at zener diodes and voltage dividers, but I'm now confused by the PICs builtin weak pull-up resistors (and if I check the datasheet, values are TBD... I assume something like 10k?)

So the PIC input pin protection circuit I think I have understood is this:![PIC input pin protection circuit][1]

But using weak pullups, I think I could do this:

![enter image description here][2]

But all this does is swap a resistor to a transistor.

**Update**

Further to comment from @PJC50, I now think the circuit utilising the PIC's pullup resistors would look like this:
![enter image description here][3]
It's now clear why I should do this and how it reduces component count.

How do I choose a resistor and transistor that are suitable?


 - Is the voltage divider circuit correct?
 - Is the circuit that uses the weak pullups correct? (i think not)
 - Why would I use pullups over normal voltage divider?

So my new circuit looks like this:
![enter image description here][4]

Update 2:

I've tested the circuit with pull ups, and I think I'm getting closer to real solution, any further comment/critique welcome!
My circuit now looks like this:

  [1]: https://i.sstatic.net/3ZcjK.png
  [2]: https://i.sstatic.net/f0Ntg.png
  [3]: https://i.sstatic.net/NHgBv.png
  [4]: https://i.sstatic.net/HuGm2.jpg