If you're doing testing, I'd just pull the steering wheel airbag out of the column and set it aside; it wouldn't hurt to disconnect the battery before doing so.
Since all you're doing here is looking for an open in the circuit, you can disconnect the clock spring on the column side completely and you should be good.
I don't know about opening up the clock spring; they are a pain to put back together right (I tried to tear apart an old one before) and all modern units use a plastic ribbon style coil these days rather than brushes/arms anymore.
(A picture I found via Google search, but all clock springs are main like this.)
If you do take the whole clock spring out to bench test it, make sure to note the timing marks (triangles) on the case these will denote the 12'oclock position of the Clock Spring, while the viewing window on the left will have an Orange or Yellow wheel that shows in the viewing window with the timing marks aligned to indicate that the clock spring is 100% forward.
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This is something I discovered when I was playing with a clock spring in parts waiting for the parts counter guy to pull a new one. I don't see any mention of it in any Toyota literature and none of my co-workers ever noticed it (we all just did the usually "count the turns" method.) I've since checked it with a few different clock springs (it seems Toyota uses basically the same design for most of their vehicles.)
This is mainly a trick I figured out for people who may have turned the clock spring off the steering wheel and are having trouble finding straight ahead.
