Hidden interface controls that affect usability

I'm pretty sure that simple switch is something directly in the circuit for the fog light, and there is a dedicated wire between the fog light, the switch, and the fuse box. And if its an old Jag, those wires flake out and have to be redone at great expense.

Compare this to the databus that is used in today's cars, it really isn't even a fair comparison on cost (you don't have to have 100 wires running through different places in your car, just one bus to 100 things and signal is separated from power).

> I'm pretty sure that simple switch is something directly in the circuit for the fog light, and there is a dedicated wire between the fog light, the switch, and the fuse box. And if its an old Jag, those wires flake out and have to be redone at great expense.

I don't really want to get into a big debate about this as I haven't worked on Jags, but I don't believe that replacing parts of the loom is would be that expensive. Remaking an entire loom, I will admit that would expensive as that would be a custom job with a lot of labour.

> Compare this to the databus that is used in today's cars, it really isn't even a fair comparison on cost (you don't have to have 100 wires running through different places in your car, just one bus to 100 things and signal is separated from power).

Ok fine. But the discussion was button vs touch screens and there is nothing preventing buttons being used with the newer databus design. I am pretty sure older BMWs, Mercs etc worked this way.

They can be used, they just need more complexity than a simple switch that completes a circuit, they now have tiny cpus so they can signal the bus correctly. The switch must broadcast turn thing on when the switch is set to on, and then turn thing off when the switch is set to off, all with whatever serial protocol being used (including back off and retry, etc. ..). So your input devices need to be little computers so that you can use one bus for everything, now you can see where one touch screen begins to save money.

I don't believe what you are describing is necessary. I am pretty sure you could have a module where the switches are wired normally into something and that communicates with the main bus. I am pretty sure this is how a lot of cars already work from watching people work on more modern vehicles.

In any event. I've never heard a good explanation of why I need all of this to turn the lights on or off in a car, when much simpler systems worked perfectly fine.

Ah, the classic "a keyboard has a CPU for each key" argument

Many of the low-speed switches are connected to a single controller that then interfaces over LIN or CAN to the car.

Reducing the copper content of cars and reducing the size of the wiring bundles that have to pass through grommets to doors, in body channels, etc. was the main driver. Offering greater interconnectedness and (eventually) reliability was a nice side effect.

It used to be a pain in the ass to get the parking lights to flash some kind of feedback for remote locking, remote start, etc. Now, it’s two signals on the CAN bus.

Depending on age, it’s more likely that the physical switch drives an electric relay and the relay switches the actual fog lamp current which could be 3-5amps per lamp, letting the manufacturer use a small gauge trigger wire to run to/from the dash and thicker wire only for the shorter high-current path.

OK, thanks for the explanation.

> Offering greater interconnected news and (eventually) reliability was a nice side effect.

I am not sure about that. You still suffer from electronic problems due to corrosion around the plugs, duff sockets and dodgy earths as the vehicle ages.

You can have hundreds of switches closing circuits all connected to a device that is connected to the can bus.