Measuring the resistance of that sort of circuit won't predict current consumption. The problem at the moment of course is you don't have a stable 12V supply. If you could even 'borrow' the battery from a car to run a single light and measure the current with your meter then you'd have an idea of what you need to do.I’m measuring 220-240 K ohms on one circuit, of six (now working) lights
That seems like a lot of ohms, but not a lot of amps?
LED lighting is pretty low power.
https://www.amazon.ca/Waterproof-Flexible-Daylight-Gardens-Kitchen/dp/B00HSF66JO
This are 18W at 12V. That means 18W/12V=1.5A
A search with these terms shows up all sorts of inexpensive AC adapters for 12V LED lighting.
https://www.amazon.ca/s?k=LED+lamp+...ed+lamp+power+supply,tools,141&ref=nb_sb_noss
And Amazon is really expensive for those sorts of things. If you can wait for Aliexpress to end of April.
Aliexpress power supply
Even Lee Valley Tools carries this sort of thing.