Back in the 1970s I had a friend who owned a Mitsubishi-built Dodge Colt. Whenever the driver’s seat belt was pulled out to its fullest extent, the dome light came on. We called it the sudden deceleration warning light.

I thought of another one.
The Jeep had a failing battery. It was only holding 11.something volts. That was still enough to start the engine at a normal cranking speed, which masked the impending battery failure.
However, when it was parked, and various power draws like the clock took the battery below some minimum threshold, one of the relays would fail to hold, and the HVAC blower would come on, and run until the battery was completely drained. Of course, hook up jumper cables, and the relay acted normally, as did the starter.
It took a trip to the grocery store to figure out what was wrong. Gone long enough for the blower to come on, but short enough that it was still running.

Working as a lot jockey at a Chrysler dealer in the early nineties, two separate times I had to drive from Mississauga, Ontario to Hamilton Ontario on some kind of dubious errand for the dealership’s crooked owner. The first time I got to take a brand-new LeBaron Turbo convertible. It was a nice, sunny day and I naturally put the top down. On the way back, I hit a freeway expansion joint at whatever speed traffic was going, not anything fast. Suddenly there was a burning smell and smoke starting coming out of the glovebox. The radio and instrument panel went totally blank but the car kept going. I got back to the dealer, parked the car, and walked away. Someone tried to give me shit for breaking the car but I just played ignorant. A month or two later I went over the same expansion joint at the speed limit in a Chrysler minivan and the exact same thing happened…

In stop-and-go summer Texas traffic, a Saturn SC2 couldn’t get enough cooling air through its diminutive bumper intake to stay cool. You could turn the A/C on, which would force the A/C condenser fan to turn on, assisting the belabored radiator fan somewhat. Of course, the load created by the A/C compressor would just cause the engine to run hotter if left on.
If traffic could only proceed, then airflow to the radiator would be sufficient for both my engine and my sweltering tissues to survive. But nope.
So that’s why I’m sitting there, repeatedly turning the A/C on and off, leaning desperately out the window to listen for fan noise and A/C clicks, while the heater is on at full blast.

I’ve been in multiple GMT800 trucks in which when you turn one way the HVAC system sends heat and when you turn the other it continues to blow cold air…cause/effect still unknown.

The motor mount breaking and causing unintened acceleration pretty well known, at least now. Millions of 60’s Chevrolets were recalled because of the fact that their mounts at the time did not incorperate a limiting mechanism that stops excessive movement when the rubber fails. So rather than replace the existing mounts with a properly engineered part the cars were outfitted with limiter cables. The bolted on with new longer exhaust manifold bolts and looped around the shaft for the upper control arm.
The reason that the shifting engine caused the car to accelerate was the use of rods to control the throttle instead of a cable. Since the rod was attached to the linkage on the firewall or to the pedal through the firewall the change of the distance between that location and the carb caused the fixed length rod to open the carb. That of course caused the engine to torque more, increasing the throttle opening causing more torque and quickly enough a engine at WOT despite the fact that there was no pressure on the pedal.
That certainly helped boost the change over to a cable in a sheath type of system which prevents the problem until the point where the cable is stretched so tight that the sheath breaks.

Had a dime fall into the lighter socket. Took more than one fuse for me to actually look in the socket.

Had an 88 Acura Interga -great car except that after I’d owned it a year it developed the weirdest problem either I or the Service Manager had ever seen. The car (a beautiful little aluminum DOHC with fuel injection) started perfectly on the first turn of the key, every time…. and then died. After a week of fussing around, the Service Manager called me and said the car was ready to pick up; they had essentially replaced the entire fuel injection system piece by piece unti they found the problem. I said, “great!” and went and picked up the car which started perfectly…and died instantly. They hadn’t found the problem after all, at least not when the car was outside in cold weather.
After another week, the Service Manager finally called and very proudly told them they’d finally found the true cause. The ignition switch had failed some how, and when you inserted the key and turned it to “start”, it connected the contacts and the car fired up perfectly. However, the switch had internally cracked somehow and when you released the key after starting the car, the key didn’t move all the way back from the “start” position to the “run” position, so contact wasn’t made and the engine -having an incomplete electrical circuit -stopped.
Replacing the ignition switch fixed the problem.

I went to turn off my 2001 outback one day, and the key wouldn’t come out of the cylinder. Brought it to a local ‘subaru specialist’ who told me that I’d need to replace the column which would be a whole mess, and just to deal with leaving the key in. I had keyless entry so it wasn’t a big deal to leave the key in. One day a few months later I go to hit the horn, and I get nothing. Upon further inspection the horn had blown. I used to have an 89 town car that had way better horns than the little japanese ones, so i had transplanted them behind the grill of the outback; the lincoln horns were of the spiral housing type, and i had to face the opening up for them to fit in the space. Turns out they had filled with water, which had then frozen, and shorted out the horn circuit when I hit the horn. Replaced the horn fuse and the key came right out.