1. ICE cars have loads of electronics in them and they, in general don't suffer from problems with heat, cold, condensation etc I Had a 2003 VW Phaeton 3.2 litre for 4 years, biggest load of rubbish ever, the electronics were always going on the blink and no VW service centre could get to the bottom of it. Gave up lost 2/3rds when I sold it. Will never touch a VW group product again.
VW, and some other companies such as PSA went through a bad patch when lead free solder became mandatory. Their electronic black box suppliers (they don't make them themselves, VW use a lot of Bosch stuff, and Bosch software engineers programmed them for them, hand in glove with VW, hence Dieselgate, hidden emissions defeat trickery etc. They hadn't done their homework on how to change their soldering methods, PCB construction etc. to work properly with the ROHS requirements. Valeo didn't seem to have either. Others had. Don't tar them all with the same brush, based on one bad experience from many years ago.
That is now long in the past.
The connectors used in automotive applications are seriously engineered things, up to or even better than the toughest military standards. Probably the most danger to them is from ham fisted mechanics not disconnecting and re-seating them properly, some require special tools, but simple, to do so. Not just trying to force back tabs with whatever screwdriver comes to hand, and not bothering to grease the seals, if that is a requirement. Or the wiring loom being chafed. But main wiring looms are so much simpler, lighter, less expensive and more reliable nowadays, now that most parts of the vehicle are controlled by serial busses.
Yes, diagnosis of weird faults can be a nightmare, even for some main dealers, not all have access to the full diagnostic equipment, nor are particularly clued up on how to make sense of what it can tell them.
Most commonly the fault are with sensors and mechanical actuators, not the powertrain and body electronics. Or bodged installations of added stuff, such as towbar electrics, sound systems, and so on.
None main dealers don't have the full kit anyway. Yes they can use third party OBD code readers, some better than others, to tell them which sensors might be faulty, then resort to parts swapping, and maybe even do some tinkering. Used to be be that the most use was to try to turn off the fault light long enough to scrape through the MoT. Or for "tuners" using reverse engineering to remap the powertrain ECU to whatever purpose.
FWIW I think that Tesla (yes I know, I am sounding like a stuck record) are vertically integrated regarding their electronics design, if it's not mostly done in house then they are certainly using specialist companies who are working well together with them.
Fundamentally the fewer moving parts, the better, as regards reliability and longevity. Electronics hardware, properly designed, can be extremely reliable. I know of what I speak, having been Chief Hardware Engineer, responsible for all electronics design (by my team), in a motorsport and roadcar manufacturer, where it was all done in house, and also supplied to many other big name companies who didn't have their own in-house expertise.
