I bought the Lucas Workshop manual, it was not cheap, and until the avant of microfiche it was auto updated with a ring binder design so pages could be added. This was back in the 70's, and we have always been able to get the manuals if we are willing to pay for them.
But in the main today no point, as the tools required mean you can't DIY even if you have the manual. So the manual says for example test with insulation tester set to 250 volt, but most DIY people will not have an insulation tester, or plug in the engine diagnosis unit into the socket found xxxx, so without that unit, rather pointless.
By 2000 the use of PLC's and PIC's was getting common, (PLC = Programmable logic controller, PIC = Programmable integrated circuit) I remember in one place I worked, a fork lift accident had smashed a PLC, and the electrician had read the part number, ordered a new one and fitted it, but it did not work, as it needed a program loading into it, the lead to connect to the PLC cost £125, the program another £350, and of course a computer was required, but also it needed the program writing, there may have been a copy of the old program, but often these things are modified so some skill is required to see if the old one still suitable.
But in the main as DIY it is a trust to the Lord, and safety checks are missed. Some times we are lucky, I remember with a welding machine it had a load of op-amps on the control board, they cost around £0.30, but the board cost £150, so we would swap the four op-amps, if it worked great, if not new board, no instruction manual is going to tell you to do that. We all do it, light stops working, we do not get the meter out and start checking switches etc, we swap the bulb first, and 99 times out of 100 that works, when it does not often you find it still was the bulb at fault, but it has when it failed opened some overload device.
I remember in collage when starting to learn about PLC's being told to write an instruction set for how to make a cup of tea, using a tea spoon ladle on spoon full of tea into the tea strainer, place in cup etc, most would miss something, like turn the kettle on. To write any instruction set, you need to assume the user has some knowledge, I have talked about that
here, what should instructions say one needs to assume the person repairing or using the item has some knowledge.
Of course this can go wrong, I remember the driver of a steam roller returned to work after a long illness just before we took delivery of a new diesel roller, as he approached the junction he put it in reverse to stop it, causing damage, the plant manager blamed the roller manufacturer for not putting a notice in the cab about the change in practice. Seems putting into reverse was a standard way to stop steam rollers, and also some other items like electric fork lifts. But as a car driver we would not dream of doing that, we hope?