This article is from the alt.usage.english FAQ, by Mark Israel email@example.com with numerous contributions by others.
"Jury-rigged", which means "assembled in a makeshift manner",
is attested since 1788. It comes from "jury mast", a nautical term
attested since 1616 for a temporary mast made from any available
spar when the mast has broken or been lost overboard. The OED
dubiously recorded a suggestion that this was short for "injury
mast", but recent dictionaries say that it is probably from Old
French "ajurie"="help or relief", from Latin "adiutare"="to aid"
(the source of the English word "adjutant").
"Jerry-built", which the OED defines as "built unsubstantially of
bad materials; built to sell but not last" is attested since 1869,
and is said to have arisen in Liverpool. It has been fancifully
derived from the Biblical city of Jericho, whose walls came tumbling
down; from the prophet Jeremiah, because he foretold decay; from the
name of a building firm on the Mersey; from "jelly", signifying
instability; from French "jour"="day" (workers paid day-by-day
considered less likely to do a good job); and from the Romany
"gerry"="excrement". More likely, it is linked to earlier
pejorative uses of the name Jerry ("jerrymumble", to knock about,
1721; "Jerry Sneak", a henpecked husband, 1764; "jerry", a cheap
beer house, 1861); and it may have been influenced by "jury-rigged".
"Jerry" as British slang for "a German, especially a German
soldier" is not attested until 1898 and is unconnected with