Fair point, I was not considering what else was on the meter fuse circuit. I think the alarm system was powering two of the coils previously through the cruise control switch before, and it did not blow any fuses with that arrangement.

Well, you convinced me. Each pair of coils draws more than 5amps at idle so it made sense to separate them out of a circuit that could shut off the main relay.

Installed a relay next to the main relay box, used the factory coil power as the trigger. Ran two separate fused lines to the coils. If one coil ever has excessive draw or a short, it will not shut down anything aside from it's batch sister coil. Added bonus, the connectors at the relay makes the wiring removable and testable, and allowing neater installation/routing as I re-do other lines and hoses under the hood.

Test drove the car quite a bit, seems to be running great, maybe even a bit smoother. No issues with repeated runs up to and at 7800 rpm, 17psi of boost. Nice. While I was procrastinating with this, I had a chance to rewire the Wideband and get rid of last of the wire nut connectors from previous owner. I believe the only wire nut connectors left are on the aftermarket oil temp and pressure gauge sensor lines.

Anyway, thanks a lot for the help. It was a nice excuse to download some wiring diagrams and get more familiar with how the electrical system is designed on a Miata :)

You do NOT want the coils to blow a fuse by themselves. If it happens, the ECU will continue injecting fuel, and you will hydrolock the engine. Put them together with the injectors.

I can see your concern. A stuck open (or leaking) injector certainly can cause hydrolock on a parked car. However street engines do not have enough flow rate to cause hydrolock with a rotating engine. If you have ever had a failed coil -with German cars it happens quite often- it is not an issue. In fact, I have a 600hp motor that uses ignition cut for traction management and no issues there either, and that's extended use at full throttle (in the wet generally). :)