My speedo (aka "cyclocomputer"), a wired Cateye with cadence, has started dropping the speed reading in cool weather (<50F). Checked the magnet alignment first, and it's fine.
My first thought was the battery must be getting old, although the display isn't fading. I thought I had a spare, so I brought it inside. Didn't have a spare, so the next morning (45F), put it back on and it worked... for about two minutes. Cadence worked fine. In the afternoon all was fine.
So I replaced the battery anyhow that evening and cleaned the contacts. Same thing: worked about 3 blocks (maybe 48F?), then dropped out for another 3 miles or so, then started working.
My thoughts are: harness, contacts, magnet, and reed switches must be working, since the whole thing works when it's warm. New battery, so the temperature can't be causing the problem.
Sigh, everything's exonerated but the problem persists. I must be missing something. What could it be?