Gotta love electricity. Go from household wiring to automotive and you have to turn some of it backwards (i.e., black goes from ground to hot).
Then there is the nature of electricity and components, which is, weird things happen. For example:
(1) By the markers running through the other bulbs for functions, they should last longer, since they were built for with future sales in mind, running at a given voltage, but, by powering them through other bulbs, the voltage is reduced and they should last longer.
(2) I had a feed back in the dash, when I stepped on the brakes. both turns would come on. ???? I scratched my head and went for the obvious - check bulbs. All of them read good. Then I looked at one and noticed something amiss. One of the double element filaments had opened. The tension it was under caused it to move wildly, and it hit the other element, where it welded to it, creating a feed back circuit between tail and turn circuits.
If my vision hadn't been good, I could have been scratching my head for a while.
(3) Then there is the raw power of ignorance. About fifty years ago, my dryer died. I had it half torn apart, trying to figure out what the problem was, until I learned it was a 240 volt appliance with two breakers, and the breaker used was an improper one lacking the double lock out. Reassembled everything, hit the breaker and never had a problem again.
(4) Years after the dryer intermittent failure, I came to learn all about loathing intermittent from working complex electrical equipment for the feds (civilian, employed by the Navy). Chasing such things has made even women bald (hair pulling).