Can I use a different voltage / amp to what the device is rated?
I wouldn't do it because you simply don't know what circutry that powers: it could be anything, and the steering wheel looks expensive enough to avoid risking a new unit.

I have this:
https://www.tooq.com/product.php?id=1521

Available for 20 € where I'm based (Madrid):
https://www.pccomponentes.com/tooq-tqlc-100bs01m-cargador-universal-portatiles-100w

It even comes in an aluminium case which is great for heat dissipation. I bought it to power a laptop from a camper van battery, as it does both AC-DC and DC-DC step up and it works really well.

Since it comes from China, maybe in Australia you can find something like that, but good for the 160 W you need.

In fact, I would check the actual consumption of the steering wheel, I wouldn't be surprised if it's well below those 6.7 A. Can you get hold of a lab power supply and a multimeter for this quick check?