Problem solved. Turns out that the person who made the original adapter had the wires mirrored (as you look at each end of the adapter), but they should be one for one. Hard to explain...
The guy who sold it sent me a temporary one that was wired correctly, and my detector sounded and acted normal, again. Quite a bit more sensitive to RFI, but it works! I ended up just taking the original adapter and re-soldering it, as the temporary he sent me did not have plug housings (I suppose that he did that so that I didn't do a 2 for 1 theft). I tried the coil today, and all seems well. Found some a quarter & two dimes, brass eyelet, and strange, broken, cheap jewelry piece. Good enough for me!
TorqueMaster, check your PMs!