Where you say, "They (the older cars) were not instrumented enough to tell you what was wrong. You ended up swapping out parts until the problem was fixed."
I'll take the other side of this one just for fun....of course we both already know it doesn't have to be guesswork.
There is another way, and that was to learn more about that peculiar mechanical/electrical system, dig deeper, and eventually find enough additional clues so that the problem more or less diagnosed itself. Next do one simple test to confirm the logic, and then just repair only the offending part.
That way had value beyond the immediate job. In fact, I wonder sometimes if we have lost something when we lost that type of self-taught technical training. The mind set that accompanies that type of repair seems to have been more common a few decades back than it is today. Years ago, every really good automotive repair shop had to have a person with extraordinary abilities in basic diagnosis - in small shops it was often the owner himself.
Part of the value was that more than a few of the repair shop owners eventually ended up doing engineering design. I know I did.
I hate trial and error approach. I experienced this when an auto shop's machine gave multi-choice for problem and solution. End result was doing the repair for both of the problems but neither completely cleared the problem.
I agree. I have ended up buying parts and parts for my car until I finally found the one causing the problem. I think the worst part (other than the wasted money) is when you think the most recent new part fixed the problem only to find out later that it didn't.
That was always a problem with older model cars. They were not instrumented enough to tell you what was wrong. You ended up swapping out parts until the problem was fixed. The problem there was that many of the parts swapped out were not bad and you have expended the money to get them. I had always bought used sports cars and worked on them myself. I was modifying them as well as repairing them. When I was having trouble getting to work with two cars and two motorcycles, I decided to buy a new car. I think my expenses went down.
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