We're fixing up a 1987 Jeep Wrangler for our son. I could strip it down to the frame with 3 or 4 tools. It's kind of amazing how simple cars were, and that was in the late 80's.
Alec of Technology Connections just posted a video on this:
This and the video on hybrids, are, imo important works, because they break things down in a way that disarms tribalism, and explain how it is that we got to where we are. There are very real stakes in ownership, right to repair, and freedom of movement that rest on people having a good baseline understanding of this stuff.
The complexity of modern vehicles comes down to software coupling between the systems, which (to my knowledge) started with automatic transmissions, and then spread to everything else. In very modern vehicles, even the sensors register with the ECU and communicate on encrypted channels.
The reason for these measures is ostensibly security and quality, but automakers don't seem to mind the fact that it also makes many repairs more difficult or impossible.
But it was easy to work on. My dad (not a mechanic) usually had a strong hunch about what the problem was. Lights went dim while you were driving and five minutes later it sputtered out? Alternator is dead. Flip through the manual to find a diagram of where all the bolts are, take it off, run to Auto Zone, get another one, bolt it on. By the end it was usually dark and I was finishing the job with a shop light hung under the hood.
I drove a series of beaters from the 80s and 90s and did all my own repairs until my mid 20s. Alternators, water pumps, break pads, break lines, ignition solenoids. All of it is just parts that you unbolt and bolt a new one on. When I got my first modern car (a 2008!) one look under the hood made me realize I had joined the yuppie class and would not be changing my own spark plugs anymore.