1) Just about any Toyota steering wheel will fit onto the steering shaft.
2) Yes, I've done it
3) Yes, he does because see #1
4) You don't need custom ordered parts, just some "replacement" airbag wire harnesses for the new airbag
5) agreed, search, but it hasn't been done by many, so you may not find a lot of info. In which case here you go...
The easiest swap(at least to me it was) will be a gen5 Camry SE wheel. like the one I have...
All you need for wiring is the harness from a donor gen3 airbag. Preferably one that hasn't been deployed like this one. Notice the burned wires. I went to salvage yard to get this part. I went back and got one from another gen3 airbag that hadn't deployed(not pictured).
You'll need a set of "replacement" wire harnesses for the new airbag. I got these from ebay. You just need the "orange" one. The yellow w/green strip is negative, and connects to the solid yellow wire of the donor airbag harness. The other wire is of course the positive, and connects to the solid blue wire of the donor airbag harness. I used solder sleeves for the connections. I think they are the best option for this, because as you heat them, they solder the wires together, and shrink to seal/protect the connection. It's going to be a bit tricky to position the harness between the airbag, and wheel so it doesn't interfere with anything, but it's doable.
You'll need to swap the cruise control lever(if you have one) form your gen3 wheel to the gen 5 wheel. The lever at the top of the picture is from the gen5. The one at the bottom is the gen3. They are the same except for the wire harness. The black wire on the gen3 lever is the ground for the horn. The tab that the wire is pointing to in the pics is where the wire will connect to. You can solder it to the tab or use a spade connector. I used a spade connector.
Here's the gen3 lever in the gen5 wheel
Now you're ready to install.
Here's the important part. disconnect the battery for at least 90 seconds to make sure the SRS is fully discharged before you start the swap. I left my battery disconnected for 30min. just to be on the safe side.
If you you've done all the above, then here's all you'll have to do for the actual swap...
1) remove the stock airbag
2) disconnect airbag harness
3) disconnect the cruise control lever
4) remove the stock steering wheel
5) install new steering wheel
6) connect cruise control lever
7) connect airbag harness
8) install airbag
9) enjoy new steering wheel

NOTE: the wire colors I mentioned are what I found in my car, and may not be the same for your car. So, don't complain to me if the colors don't match what you have. YOU HAVE BEEN WARNED!!!
Hmm...could this be sticky worthy?
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