Unless fuses have protected your 12VDC items you may have several surprises once you start looking at all of your connected 12VDC items.
This is a typical 30AMP wiring configuration showing what is connected to the 12VDC Power Distribution Panel. Hopefully the 12VDC fuses blowed on this 12VDC distribution panel... You will need to find at least all of these items that are connected to the 12VDC Distribution Panels and check them. If those items were not turned on by you when connected to the 24VDC they should be ok. The DETECTOR boards for the fridge, furnace, CO detector, etc are most likely blown as they are connected to 12VDC all the time. If you turned on the ceiling lights they may have burned out on you.

Would be interesting to know what you found...
wishing you good luck on what you may find...
Roy ken