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Stock main relay for NA/NB

Stock main relay for NA/NB

Regular price $32.99 USD
Regular price Sale price $32.99 USD
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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.


Instructions are not currently available.


$9.99 flat rate shipping. Orders over $40 ship for free in the US!

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What does it fit?


Emissions do not apply.


1 year



Customer Reviews

Based on 4 reviews
If you own a miata you need a spare in your glove box

This is one of those "not if, but when" things. Like the description says; they fail without warning and it might fail when you're parked in your garage or when you're meeting someone to buy a set of shocks for your jeep at a gas station in the middle of no where... Glad I had a spare that day and ordered a new one as soon as I got the car started, FM ships them extremely fast which is great!


Shipped fast, arrived fast. Great product. Still tracking down some electrical gremlins, but I have progress/improvement after installing this. I'll be shopping again when I need something.


Much needed for my who knows how old relay… Mazda OEM Part great replacement.


Came in fast. Thanks