Rywire B Seris Adapter Harness for 99-00 Honda Civic

Rywire B-Series Adapter Harness - 1999-2000 Honda Civic (EK, incl. Si)

The 99-00 Civic is a favorite for B-series builds, and it's the one that came with the Si, so a lot of these cars are already halfway to being something fun. Whatever trim you started with, the wiring is where a swap either goes smoothly or turns into a weekend you'd rather forget. This Rywire adapter harness is built specifically for the 99-00 EK chassis and pairs with Rywire's B-Series Budget Engine Harness, so you get a purpose-made connection instead of cutting into your car's factory wiring and hoping for the best.

Make Sure You're Buying The Right Year

Check this before anything else. The EK Civic split mid-generation on its electronics, and the 99-00 cars aren't wired the same as the 96-98 cars. This harness is made for the 1999-2000 chassis. If your Civic is a 96, 97, or 98, you need the version built for those years instead. It's a two-second check on your title or door jamb, and it saves you a return and a stalled build. Get the right year and everything downstream gets easier.

Covers Every 99-00 Trim, Si Included

This fits the whole 99-00 Civic lineup: CX, DX, EX, GX, HX, LX, Value Package, and the Si. That's worth noting, because plenty of B-swaps start life in a base-model car and plenty of others start in an Si that the owner wants to take further. Either way, this adapter is built around what your chassis wiring actually looks like, so the connections land where they're supposed to instead of leaving you decoding wire colors with a multimeter and a forum thread.

It's The Chassis Side, Not The Engine Side

Worth being clear about, since harness terminology gets muddy. The engine harness is the one that lives on the motor itself. This piece is the adapter that ties that harness into your Civic's factory chassis wiring, letting an engine your car never came with communicate with it properly. It's designed to work with Rywire's B-Series Budget Engine Harness, so plan on having both parts in hand. This one alone won't complete the swap, it's one half of a two-part solution, and knowing that up front keeps your build moving.

Keep Your Factory Wiring Intact

You could splice your way through a B-swap. People do it every day. But every cut and every taped joint is a spot that can go intermittent later, usually at the worst possible time, and diagnosing a hacked-up harness is genuinely miserable work. Going the adapter route keeps your chassis wiring original and reversible, which matters if you ever want to return the car to stock or sell it to someone who cares. It's also just faster, and it leaves the car in a state that the next person to work on it, probably you, won't curse at.

Who Should Run This Adapter Harness

This is for anyone dropping a B-series into a 99-00 Civic who wants the electrical side handled properly the first time. Maybe it's a base-model car getting a real engine, maybe it's an Si you're pushing further, maybe you're just tired of hearing swap horror stories about wiring. Grab this along with the matching Rywire budget engine harness, plug things in where they're meant to go, and spend your weekend on the parts of the build you actually enjoy.

Fits: 1999-2000 Honda Civic (EK), CX, DX, EX, GX, HX, LX, Value Package, and Si. Type: B-series adapter harness, chassis side. Designed for use with: Rywire B-Series Budget Engine Harness. Important: not interchangeable with the 1996-1998 Civic version, confirm your year before ordering.