Ignitions and Electrical› Wiring Components

Flyin Miata

Stock Main Relay

$36.99

SKU: B5B4-18-811

In Stock
In Stock
Ships by Sep 12
Free Shipping over $200
$100 Minimum Order
30 Days Return
INSTALL DIFFICULTY
DIY PRO SHOP

Beginner — under 30 min

Overview

The Flyin Miata B5B4-18-811 is a stock main relay for NA and NB Miatas. This mechanical relay powers critical systems like the ECU, fuel pump, and ignition.

Over time, these relays can fail, leading to immediate engine shutdown and preventing the car from starting. Higher power fuel pumps can also accelerate wear. It is recommended to replace the relay as preventative maintenance or keep a new one in the glovebox. If the socket in the fusebox is corroded, cleaning it is advised to prevent heat buildup from increased resistance.
Show original supplier description
The Flyin Miata B5B4-18-811 is a direct replacement stock main relay designed for NA and NB Mazda Miatas. This essential component powers crucial vehicle systems, including the Engine Control Unit (ECU), fuel pump, and ignition system. Mechanical relays, like this one, are prone to wear and tear after decades of use, and can fail without warning. When a main relay fails, it typically results in the engine stopping abruptly, potentially leaving the vehicle stranded. This failure can occur while driving or prevent the car from starting altogether. Higher-current aftermarket fuel pumps can exacerbate the wear on the stock relay, hastening its demise. Replacing the relay proactively or carrying a spare in the glovebox is a common preventative measure. When replacing the original relay, inspect the fusebox socket for corrosion. Cleaning any corroded contacts is recommended to ensure proper electrical connection and prevent heat buildup, which can be caused by increased resistance. This particular relay is a factory replacement for 1996-2005 models and is compatible with all NA/NB Miatas, including the 1990-1997, 1999-2005, and 2004-2005 MSM variants. For vehicles with higher power fuel pumps or upgraded ignition systems, an 80A version is recommended.

Product descriptions are provided by our supplier partners and may not always be perfectly accurate. Not sure this fits? or call (760) 282-4645 and we’ll verify before you order.

Fitment

Fitment Guaranteed

Don’t gamble
on fit.

Log your build in the MOTORMIA app and we’ll guarantee this part fits your exact setup — or your money back, return shipping covered.

Available on iOS & Android

Specifications

BrandFlyin Miata
Part NumberB5B4-18-811
CategoryIgnitions and Electrical

We’re here — turning wrenches, just like you.

Call us, follow along, or come say hi.

(760) 282-4645 Instagram Google

Buy with Confidence

Returns & Fitment

Built for enthusiasts. Every order is backed by our 30 day return window on eligible items. Unused and uninstalled products may be returned with approved RMA and no restocking fees when received in new condition. Orders placed through the MOTORMIA app with a complete build qualify for our Fitment Guarantee — free return shipping if the part doesn’t fit your exact setup. The guarantee covers fit only; installation must follow manufacturer instructions, and we recommend a qualified shop for parts marked Difficulty 4–5.

View Full Return Policy

Shipping

Orders are processed in 1–3 business days. In stock parts ship promptly from our partner network. Special-order items either aren’t currently stocked or are built to your spec — expect 4–6 weeks. If a part goes on backorder while your order is in the queue, we’ll reach out and work through discounted alternatives together.

Free shipping over $200 in the continental US. Alaska, Hawaii, U.S. territories (Puerto Rico, U.S. Virgin Islands, Guam, American Samoa, and the Northern Mariana Islands), and international orders carry surcharges — most appear at checkout. Some exceptions (LTL freight, or suppliers who quote freight only after we place the order) won’t. In those cases we’ll reach out with the exact charge before your order moves forward.

View Full Shipping Policy