And this one from not to long ago where the main cable from the engine generator had been run on finger tight on phase A so it got so hot it melted out the lug
Years ago I used to own a share of a Piper Warrior (160hp, 4cyl single engine). We had problems with the alternator tripping off - assumed to be the over-voltage trip* operating. After months of "we'll try ..." from the so called engineers, I called them up and said "I'm coming down, I'm going to strip, clean, and reassemble all the connections in the battery and charging circuit"** - note, not a "can I" but an "I am". Of course, they started with all the "we'll have to check your work" (I said "fine"), etc., etc. reasons why I shouldn't. When I arrived, they said "can you take it for a test flight, we think we've found the problem" - I did, and they had.
I was 'kin livid, and had it been down to me I'd have made quite a stink about it. There was a bad crimp on the alternator field connection - when it was high resistance, the regulator would crank up the field voltage to compensate, then when it went low resistance, it would cause a higher than needed field current which would trip the over-voltage protection before the regulator could turn the field down. It had been crimped with a pair of pliers, or one of those plier type crimping tools - cut connector in half, found flat oval cross section rather than squeezed down to a gas tight connection. The tell-tale was about an inch of the white insulation was grey. And for good measure, one of the mechanics innocently commented that he'd noticed that when replacing the alternator during one of their previous "we'll try ..." steps.
I don't know how much it cost us in parts and labour - for one bad crimp that one of their own engineers had noticed some time before this came to a head.
* Typically on these small aircraft, there is both a voltage regulator that controls the field current to maintain a constant battery/bus voltage, and an over-voltage trip that cuts the alternator field if the voltage goes above a certain threshold (to prevent a disconnected battery from frying all the electronics). Sometimes they are separate units, more typically both functions in one module.
Also, unlike cars, the alternator is not self-exiting - it's field comes from the battery/DC bus via a switch and an external regulator.
** I'd been asking friends and been advised that a common reason for this problem was a bad connection that caused intermittent connection, and hence intermittent alternator issues.