Best Automotive Relay Box Kit (2026): 6-Circuit and 3-Circuit Picks

Adding lights, fans, horns or a fuel pump to a vehicle usually ends the same way: a tangle of loose wires, inline fuses and relays hanging under the hood, with no easy way to tell which circuit is which. A relay box gathers that sprawl into one labeled, covered block, so each accessory gets its own relay and fuse in a known place. This guide compares the best automotive relay box kit options by circuits, relays, fuses, protection and size, from six-circuit waterproof blocks to a compact three-circuit box for a small build.

GarageToolHQ earns a commission when you buy through links on this page, at no extra cost to you. Read our affiliate disclosure.

Picks for the garage

#	Product	Shop Score	Buy
1	True MODS 12V Automotive Waterproof 5-Pin Prewired	9.5/10	Buy on Amazon
2	Nilight 12V Fuse Relay Box 6 Relays 6 Slots	9.5/10	Buy on Amazon
3	Weasch 12V 6 Way Pre-Wired Fuse Relay Box Kit	9.4/10	Buy on Amazon
4	Weasch 12V 3 Way Pre-Wired Fuse Relay Box Kit	9.3/10	Buy on Amazon

1

True MODS 12V Automotive Waterproof 5-Pin Prewired

ONLINE LED STORE·9.5/10 Shop Score

i

The Shop Score runs from 9.2 to 9.8 and weighs performance (35%), build (25%), value (25%), safety (10%, where it applies) and warranty (5%), using only what the manufacturer and the listing publish. How we pick ›

A 6 gang waterproof relay and fuse box with six 5-pin Bosch-style relay sockets, 10 fuses, 12 AWG power wires and an IP65 rating, for 12V vehicles.

Check price on Amazon

Pros

• Six 5-pin relay sockets with six fuse holders
• IP65 waterproof rating with nylon 66 construction
• 12 AWG power wires with 16 AWG pigtails
• Color-coded labels, silicon seals and a 6-wire-to-1 terminal ring

Cons

• No warranty term is stated
• No safety certification or listing is stated
• Largest block here at 7.88 inches by 7.13 inches by 4.25 inches
• Relay amperage given as a 30A and 40A range, not per slot

2

Nilight 12V Fuse Relay Box 6 Relays 6 Slots

Nilight·9.5/10 Shop Score

i

The Shop Score runs from 9.2 to 9.8 and weighs performance (35%), build (25%), value (25%), safety (10%, where it applies) and warranty (5%), using only what the manufacturer and the listing publish. How we pick ›

A pre-wired 6 relay and 6 fuse box with five 5-pin and one 4-pin 40A relays, six blade fuses and waterproof top and bottom covers, for 12V vehicles.

Check price on Amazon

Pros

• Six relay slots and six fuse slots for six circuits
• Five 5-pin and one 4-pin 40A relays included
• Six ATC and ATO blade fuses from 5A to 30A
• Waterproof and dustproof top and bottom covers

Cons

• No warranty term is stated
• No safety certification or listing is stated
• Only one 4-pin relay among five 5-pin relays
• Mounting needs wall space on both sides for the brackets

3

Weasch 12V 6 Way Pre-Wired Fuse Relay Box Kit

Weasch·9.4/10 Shop Score

i

The Shop Score runs from 9.2 to 9.8 and weighs performance (35%), build (25%), value (25%), safety (10%, where it applies) and warranty (5%), using only what the manufacturer and the listing publish. How we pick ›

A 6-way pre-wired fuse and relay box with four 40A 4-pin relays and six blade fuses, a 25A continuous load limit per circuit and a 64A total cap, for 12V vehicles.

Check price on Amazon

Pros

• Six fuse slots with fuses from 5A to 30A included
• Double overcurrent protection with fuses in series
• Pre-wired color-coded harnesses for a plug-and-play install
• Suits headlights, fog lights, horns, pumps and fans

Cons

• No warranty term is stated; the listing states no warranty
• No safety certification or listing is stated
• Only four relays for six circuits
• Dustproof only; not completely waterproof

4

Weasch 12V 3 Way Pre-Wired Fuse Relay Box Kit

Weasch·9.3/10 Shop Score

i

The Shop Score runs from 9.2 to 9.8 and weighs performance (35%), build (25%), value (25%), safety (10%, where it applies) and warranty (5%), using only what the manufacturer and the listing publish. How we pick ›

A compact 3-way pre-wired relay box with three 80A 4-pin relays and three blade fuses, a 30A continuous safe load per circuit and dustproof covers, for 12V vehicles.

Check price on Amazon

Pros

• Three heavy-duty 4-pin 80A relays included
• Double overcurrent protection with fuses in series
• Pre-wired color-coded harnesses save crimping work
• Suits lights, horns, audio, pumps, fans and LS swaps

Cons

• No warranty term is stated; the listing states no warranty
• No safety certification or listing is stated
• Dustproof only; must not be exposed to water
• Only three circuits, the fewest here

Compared on paper

Every rating comes from the brand’s listing and is not a shop test (gathered 30 October 2026).

How the points were given

Each relay box is scored on performance, build, value, safety and warranty, with the weights published on the method page. A stated safety certification earns safety points; a concrete warranty term earns warranty points. Where a listing states no certification or term, those points stay at zero.

No score drops under 9.2 or climbs past 9.8; a tool’s place inside those bounds is set by its weighted point total.

What the listings tell you

The group splits into six-circuit blocks and one three-circuit box, all pre-wired for 12V vehicles. Relay ratings run from 30A and 40A to an 80A peak, but the continuous limits the listings state are lower, which is the number that matters for a real accessory. Protection splits too: two boxes claim waterproofing, while two are dustproof only and must mount in a dry spot. Fuse counts run from 3 to 10, and two listings give dimension figures in both millimeters and inches that do not agree.

Buying guide: best automotive relay box kit

Circuits and relays

Count the accessories first, then the circuits. A six-circuit box suits a build with lights, fans, horns and a pump, while a three-circuit box suits a single project like a light bar and a fan. Relay counts do not always match circuit counts: one six-way box includes four relays, so two circuits need relays added, while another includes six relays for six circuits. Check the included relay count, not just the slot count.

Continuous load vs relay rating

The relay rating is not the system limit. One listing pairs 80A relays with a 30A maximum continuous safe load per circuit on 4mm wires, while another pairs 40A relays with a 25A maximum continuous load per circuit and a 64A total cap across all circuits. Always verify the accessory amperage against the continuous limit and the wiring diagram before connecting, since the wire gauge sets the real ceiling.

Waterproof vs dustproof

Mounting location follows protection. One box carries an IP65 waterproof rating with nylon construction and silicon seals, and another uses top and bottom covers for waterproof and dustproof protection. The other two are dustproof only: one must not be exposed to water or immersion, and the other handles light splashes but must mount in a dry location away from direct rain. Under-hood mounting needs the waterproof boxes; cabin mounting suits the dustproof ones.

Pre-wired vs unwired

Every box here arrives pre-wired with color-coded harnesses, which saves crimping and prevents connection errors, and two listings also offer an unwired version for custom heavy-gauge projects. Pre-wired suits a straightforward install; unwired suits a builder who wants heavier wire for a higher continuous load than the pre-wired gauge allows.

Mounting and dimensions

Check clearance before ordering. Boxes here range from a compact dustproof unit to a larger waterproof block measuring 7.88 inches by 7.13 inches by 4.25 inches, and brackets vary from side brackets to Z-shaped brackets for under-hood mounting. Two listings give dimensions in both millimeters and inches that disagree, so use the bullet figures and confirm clearance for the bottom wire exits as well as the box itself.

Garage Fit Check

• Space: the largest block measures 7.88 inches by 7.13 inches by 4.25 inches, while the compact three-way box is the smallest here, so measure the mounting spot first.
• Power: all four boxes are for 12V vehicle systems; verify each accessory amperage against the continuous load limit for its circuit.
• Storage: keep spare blade fuses and the user manual with the box, since fuse sizes vary by circuit.
• Before the first job: confirm mounting clearance including bottom wire exits, confirm whether the box is waterproof or dustproof only, and check that the relay count covers every circuit.

FAQ: garage tools

What is an automotive relay?

A relay is an electrically operated switch that lets a small control signal switch a larger circuit, so an accessory like a light or fan runs through the relay rather than through a dashboard switch. A relay box gathers several relays and their fuses into one block for multiple accessories.

How do automotive relays work?

A relay uses a control signal to close a switch for the accessory circuit, with a fuse wired in series so the fuse blows first if the circuit surges. The listings here describe that double overcurrent protection on two boxes, where the fuse protects the accessory from power surges.

How do you wire an automotive relay?

These boxes arrive pre-wired with color-coded harnesses, so wiring means connecting the labeled wires to the accessory and power source rather than crimping from scratch. The listings direct buyers to verify accessory amperage and refer to the wiring diagram before connecting, and to respect the continuous load limits.

How do you check whether a relay works?

The listings here do not state a relay checking method. What they do state is the fuse-first protection: if a circuit stops, check the blade fuse for that circuit, since the fuse is wired to blow before the accessory is harmed. A multimeter guide covers electrical diagnosis in more depth.

What size relay box do you need?

Match the circuit count to the accessory count, then check the continuous load: a three-circuit box suits a small build, while a six-circuit box suits several accessories. Watch the limits: one box caps continuous load at 25A per circuit with a 64A total cap, and another caps it at 30A per circuit, so a high-draw accessory may need its own heavier circuit.

Related: the best automotive multimeter for car audio and the diagnostics and electrical hub.