Do you have the ability to measure the voltage while the steering wheel should be powering up? Measuring the power supply voltage unfortunately doesn't really tell you much, because if there is no current being drawn while the thing is actually defective, it can suggest perfect operation, whereas, when the steering wheel should be powering up and you see the voltage drop significantly, you might be a little wiser.
1. Measure the terminals at the board upon power up or
2. Take a ceramic resistor to act as a device that's causing a current draw (one of those big white square resistors).
Next step if previous is ok: measure the current drawn between the supply and the device requesting this current.
Take the maximum output as a threshold, anything well below that (and I'm talking milli-amps above or even a full zero here) and you might be looking at a power supply that seems to behave right, but actually isn't.
If that's true, try to look inside the powersupply and see if there are worn out capacitors