[uncle_bob]

Does the orientation matter, i.e. 12v to the positive output, or 12v to the negative output?

Hi Nowra.

Yes it needs the polarity connected correctly.
Unless you want the magic smoke to escape.

I'm a bit concerned that you are asking this question as really this project probably shouldn't be undertaken by someone without even a basic electronics understanding.

If you have all the parts, you can sent them to me with return postage paid, then I can assemble it for you free or charge.