The main relay powers your ECU, fuel pump and your ignition system, amongst other things. And when they fail, you're stuck. It's a mechanical relay, and after a couple of decades they just get tired. Higher power fuel pumps will also draw more current and will hasten the failure.
Typical failure is immediate. The car will be working fine, then it simply won't start. This will strand the car wherever it sits - at a restaurant, at the beach, in your garage. We've even seen them fail mid-drive, which just shut the car down. Once the relays fail, they almost never come back.
Luckily, it's an easy fix. Swap out your relay as preventative maintenance or toss a new one in the glovebox. When you do remove the original, take a good look at the condition of the socket in the fusebox. If it's corroded, we recommend cleaning it to prevent a recurrence. Increased resistance from corrosion means more heat.
This relay is a factory replacement for the 1996-05 models but will fit all NA/NB Miatas. If your car is mostly stock, it's an affordable option. If you have a higher power fuel pump or uprated ignition system, we recommend the 80A version. If you really want to bombproof your car, look at our Trackspeed fuel pump rewire kit.
Mazda part B5B4-18-811. Fits all NA and NB Miatas.