Transient currents or current reversals can do weird arcing, especially at (exclusively at?) these mechanical connections that may be a tad loose after a few (hah! 40+) years.

You want to know something really odd? My wife's Chebbie Cavalier (wagon) has the typical side-post battery connections. About once a year (usually when it's cold) one of us will go out and get a normal start-up sequence but get the dreaded "CLUNK" followed by absolutely no power whatsoever.
Turns out, the connector comes ever so loose due to vibration and it arcs under the heavy starter load. Instant oxidation of current path and no more juice...
A "quick" dismount/mount of the terminals (always the "hot") and all is well for another year.

LED bulbs...

Lots of fly-by-night copycats have jumped on the LED bandwagon now that consumer acceptance is on the rise. Beware.
LED light output is individually less than for incandescent so you need a fairly large "array" to get good results. Also be certain to use the correct color as putting a red LED behind an amber lens will kill the visible output.

Some manufacturers put all the LEDs in series and use a internal or separate transformer to boost the voltage to the unit. Most gang together several groups of series LEDs in parallel to get the desired output (LEDs are voltage sensitive and need 1.5v -I think, could be 3v- to work, therefore they are ganged in series to make 12v useful).

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Mike!