Last night I noticed my truck’s taillights weren’t working. (Brakes and turn signals were fine.) I replaced the fuse, but it immediately blew again. So this morning, in search of the evident short circuit, I took apart the taillights. The bulbs were fine. The circuit still shorted out with the light assemblies unplugged, ruling out corroded sockets.
Turned out, the short was under the dash. An unused wire in the radio head unit wiring harness was making contact with the metal of the dash framework. It was the only wire missing any insulation – just a nick – and, of course, it also happened to be a hot wire that was making contact with ground at that spot. Taped it up and the gremlin is dead.
(It’s weird that the radio is on the same circuit as the taillights – but I got the idea to check from a few clues the web turned up for similar symptoms, so apparently it’s not too unusual.)
In higher-mileage vehicle news, yesterday I recentered the bottom bracket on my main bike. Basically, I moved it starboard a millimeter or so. This evened out the clearance between the cranks and the chainstays; previously, the drive-side crank was pretty close to the chainstay. (The cranks are the arms the pedals are attached to; the chainstays are the parts of the frame parallel to the ground that flank the rear wheel.) The asymmetry was due to my inattentiveness when reassembling things after a previous teardown.
I make problems so I can fix them! But, that’s how you learn to get all you can out of a system.
Like the Millennium Falcon.