Thanks for the comments. In any case, good luck with your initial idea and any follow-up projects!
Depending on what other projects you have in mind, you should clarify for yourself what you want to enable others to do (like making their own copies of something, or making modified designs), and what you might want to stop others from doing. That will inform whether you should seek trademark or patent protection, for example. For simple hardware projects, you probably don't have any protection anyway and do not have much you could "license" under some open-source license:
For physical objects like test leads, breadboards etc., protection via copyright is not possible. Protection via a patent (which protects the
function) is possible in principle, but has a high hurdle of "novelty and inventive step", and is quite expensive. I don't think your test leads would be considered inventive, for example, so patent protection is out. That leaves design patents, which protect the
unique visual appearance of an item. Easier to obtain, but easier to circumvent by shaping a copied product a bit differently.
Without either a patent or a design patent, you can't really "license" anything for a pure hardware product, whether open or closed source. The Wikipedia article on Open Source gives some initial guidance:
https://en.wikipedia.org/wiki/Open-source_hardware#Licenses.
So if all you want to achieve via the Open Source approach is to ensure that no 3rd party comes along, claims the design as their own, and tries to put a patent or design patent around it -- just
publish your design, in a way where you can prove the content and the date of publication. Putting the design files onto a website is fine if that website is publicly accessible and keeps a record of the history. Github probably qualifies, or you could make sure that your own website is captured by the Wayback Machine.