It looks obvious

The situation you are in is no different from any other tech writer. The technical writing process:

1. Ask engineer how the damn thing works.
2. Deafing silence.
3. Crickets.
4. Tumbleweed.
5. Just start writing something. Anything.
6. Give this something to the engineer.
7. Watch engineer become quite upset at how badly you’ve missed the point of everything.
8. As the engineer berates you, in between insults he will also throw off nuggets of technical information.
9. Collect these nuggets, as they are the only reliable technical information you will receive.
10. Try like hell to weave together this information into something enlightening and technically accurate.
11. Go to step 6.