An article about a rundown neighborhood said that “most of the buildings are jerry-rigged structures of corrugated aluminum.” Another article said that a company had “jury-rigged the aircraft with a missile in a demonstration flight.” A third said that “the whole deal is jerry-built, and far from complete.” And a fourth said that the tax system “is now a jury-built, temporary system.” Only one of those is correct; well, maybe two.
Something improvised as a temporary fix is “jury-rigged.” First used in the seventeenth century, according to the Oxford English Dictionary, “jury-rig” is a nautical term, not a legal one. A temporary mast to replace one that has broken is a “jury mast”; attaching any rigging to that is “jury-rigging.”
Something that is “jerry-built,” though, is shoddily built, usually out of inferior materials. The OED traces that phrase to 1869. (It’s not “gerry-built,” unless the builder is named Gerry.) The temporary “doughnut” tire that most cars carry these days would be a “jury-rigged” solution to a blowout; let’s hope it wasn’t “jerry-built,” too.
To be fair, things can be “jury-rigged” and “jerry-built,” meaning temporary and lousy, and it’s sometimes hard to tell the difference.
But if you conflate the two phrases and making something “jerry-rigged” or “jury-built,” you’re guilty of idiom mangling. If you rig the jury, though, you might get off lightly.