There isn't a lot of info about how they work and what parts need to be sourced so here are the basics:
How to tell if you have a heated steering wheel?
If you put drivers seat heating on and your wheel gets warm as well you have a heated steering wheel.
They only came in 4 spoke wheels and unlike the seats, there's only on and off control for the heat, as soon as you put your heated seat on 1, the wheel fully heats up. Both FL and Pre-fl cars came with heated wheels.
How to tell a non heated steering wheel from a heated steering wheel when looking for one?
You will see extra wiring coming out of the bottom left spoke of the 4 spoke wheel(bottom right on FL1 wheels).
The green or sometimes blue wires are the temperature sensor wires, whereas the black wires are the power wires for the heating element.
You can easily check if a heated steering wheel works out of the car by doing a continuity test on the 2 pins of the black heating element cable, if there's no continuity, its 100% broken.
The other part of the heated steering wheel system is the clock spring, its a special clock spring with extra wires going to and from it as well as slip rings because a normal flex cable inside can't carry the current.
Front pic of a heated clock spring with extra wiring for heat power:
Back of a heated clock spring, notice the extra 2 pin connector:
This picture shows a heat clock spring for a pre-fl car, notice the extra wires at the top:
This is what the slip rings and brushes for heating look like:
And the 2 brushes:
The temperature sensor is a negative thermal coefficient thermistor, meaning the resistance goes up as temperature goes up non linearly and that's what controls the heating element and ensures it won't overheat.
It looks like this:
And lives roughly here:
The heating element lives under a layer of roam, which is under the leather of the wheel. It's basically a thin wire spread across the wheel in a zig-zag pattern, it goes all around the wheel, and even on the spokes, so no matter where you touch the wheel it will be warm.
Pictures of the heating wire:
This picture shows a bare wheel with the heating element removed, you can still see the pattern though:
Is it possible to make a 3 spoke heated steering wheel? I'd say yes although it won't be cheap.
