While doing the clear corners and "fixing" the fog lights, I also installed a grounding kit from Z-Enterprises (maxground) after reading a number of reviews on it helping the engine to idle smoother. Yeah, they primarily do stuff for the Nissan Z cars, but the RX-8 stuff looked good, too.

This is the full kit with 4 wires with crimped connectors. The crimps were very tight on the wire.

The ends of the crimps are numbered so you can figure out which wire goes where. The numbers are only stamped on one side, so you can orient the connector such that the numbers are not visible.

This is the full kit installed. The kit came with 3 color pages of instructions that were very good (which of course I didn't follow, but I think its a guy thing). I did like the instruction in the Preparation section "Don't drop anything -- you may not find it", which is very true, especially with the bolt on the engine. The new cables duplicate the cables already existing from Mazda (the directions have you leave the factory cables in place).

The first cable runs from the battery to the ECU ground near the passenger side of the front strut tower bar. The second cable goes from the ECU to the chassis ground next to the windshield washer fluid bottle.

The third cable goes from the chassis ground to the engine.

The fourth cable goes from the engine to the chassis ground on the driver's side next to the master brake cylinder.