Yes last night we took the battery cables off to clean them to make sure it was corrosion (they weren’t that bad) but when we were hooking them back up we put the cable on the negative post and it did give a little spark?Time to find the short!
Now for possible bad news! New means nothing, if the batteries were destroyed by over discharge.
Disconnect all loads, then use the multi meter and check for continuity (Batteries out of circuit). Alternate leads! By doing this you are looking for failed diodes, and shorts, in general. Replace each fuse one at a time, alternating leads as above, till all circuits are cleared.
A short need not be a complete failure, but will be quite obvious. Just curious, did you get sparks when you connected the new fully charged batteries?