I installed a Painless Performance CirKit boss auxiliary fuse block (CirKit Boss Auxiliary Fuse Block/7 Circuits (3 Constant 12V - 4 Ignition 12V)Details | Painless Performance). It has 3 constant hot and 4 ignition leads that all run 20A fuses. And it's 12v ignition is via a fuse plugin off the hot side of the fuse for the cigarette lighter.
Can I run just run the always on and ignition wiring for the A9L through it? I like the added safety of the fuse but I could always run a relay off of it if necessary.

 

Not sure as I used a Painless Wiring engine harness but also used the factory Miata main fuse box ..
but .....
I do seem to remember something about not getting your switched power directly from the ignition wire because it can back feed the ignition and keep the car from shutting off.
Could be wrong though.

I got my switched power by tapping into one of the fused connections on the main Miata fuse box that sits inside the engine bay.
Can't remember which but at the time I used my tester to verify the wire was only hot with the ignition switched on.