Best 12V Automotive Relay Tester (2026)

The fuel pump stays silent when the key turns, the headlights refuse to come on, and the fuse box looks fine. Before swapping parts at random, a home mechanic reaches for the best 12v automotive relay tester to find out whether the relay itself is the fault. This guide compares five relay tools by pin fit, voltage range, readouts, kit contents and warranty terms, so the next electrical job starts with a clear answer instead of a guess.

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	KONNWEI KW371 6V/12V/24V Battery Tester & 4/5Pin	9.7/10	Buy on Amazon
2	Innova 5420 Power Circuit Tester for Automotive	9.6/10	Buy on Amazon
3	Automotive Relay Tester with Relay Puller	9.4/10	Buy on Amazon
4	RVMARINEPAT Relay Bypass Switch 9038 Relay Tester	9.4/10	Buy on Amazon
5	Sound Troubleshooting Automotive Relay Tester 4	9.4/10	Buy on Amazon

1

KONNWEI KW371 6V/12V/24V Battery Tester & 4/5Pin

KONNWEI·9.7/10 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 2-in-1 battery and relay tool for 6V, 12V and 24V systems, with a 10 to 2000 CCA range, a 5 to 220 Ah range, a graphical waveform display and 18 language options.

Check price on Amazon

Pros

• Covers 6V, 12V and 24V batteries plus 4-pin and 5-pin relays in one tool
• Three checks in one pass: battery health, cranking and charging
• 10 to 2000 CCA and 5 to 220 Ah ranges cover motorcycles, cars, trucks and boats
• 18 language options and a graphical waveform display

Cons

• The listing gives two different size figures in different places
• No relay puller is listed in the kit
• USB report printing is listed for Windows only
• Relay diagnosis is limited to 4-pin and 5-pin relays

2

Innova 5420 Power Circuit Tester for Automotive

Innova·9.6/10 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 power circuit probe that applies 3V, 5V, 12V or 24V, with a 45-degree swivel head, a 1.25 in backlit LCD and a 20 ft cable.

Check price on Amazon

Pros

• Applies 3V, 5V, 12V or 24V to activate components
• 45-degree swivel head reaches tight spots
• 1.25 in backlit LCD with LED polarity indicators
• 20 ft cable gives room to move around the car

Cons

• No warranty term is stated
• No relay pin fit is stated
• No puller or clips are listed in the kit
• The 1.0 lb weight is the heaviest stated here

3

Automotive Relay Tester with Relay Puller

Sound Troubleshooting·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 dedicated 12V relay unit for 4-pin and 5-pin relays, with automatic pin detection, green and red LED readouts and a relay puller in the kit.

Check price on Amazon

Pros

• Automatic pin detection and one-button operation
• Green LED for a good relay, red LED for a bad one
• Relay puller included in the kit
• Works with 11V to 15V batteries and coil resistance above 20 ohms

Cons

• Not intended for use with all BMW relays
• No warranty term is stated
• 12V only, no 24V coverage
• No display beyond the two LEDs

4

RVMARINEPAT Relay Bypass Switch 9038 Relay Tester

RVMARINEPAT·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-pack relay bypass kit that replaces 9036 and 9037, with 20 amp continuous and 30 amp surge capacity at 12V for direct control of fuel pumps, window motors and headlights.

Check price on Amazon

Pros

• 6-pack covers three sizes in two series, 9036 and 9037
• 20 amp continuous and 30 amp surge capacity at 12V
• Direct control of fuel pumps, window motors and headlights
• Fits Audi, BMW, Volkswagen, GM and Chrysler

Cons

• No LED readout or pass/fail signal
• No warranty term is stated
• Spec table lists 0.39 in dimensions that do not match a 6-pack kit
• It bypasses the relay rather than checking it

5

Sound Troubleshooting Automotive Relay Tester 4

Sound Troubleshooting·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 small handheld 12V relay unit for 4-pin and 5-pin relays, with automatic detection, green and red LED readouts and battery clips.

Check price on Amazon

Pros

• Automatic detection of 4-pin and 5-pin relays
• Green LED for a good relay, red LED for a bad one
• Small handheld shape for on-the-go jobs
• Battery clips included for direct connection to the 12V battery

Cons

• No relay puller is listed in the kit
• Not intended for use with all BMW relays
• No warranty term is stated
• 12V only, no 24V coverage

Best 12v automotive relay tester: compare the picks

We copy each listing’s rated specs exactly as the manufacturer gives them; as of 12 November 2026. Where a listing contradicts itself, both figures are shown.

How the points were given

Each relay tool is scored out of 10 on performance, build, value, safety and warranty, with the weights published on the site’s How We Pick page. Two list a stated safety feature, so two carry a safety score, and one gives a clear warranty term.

The displayed number is the weighted point total scaled linearly between 9.2 and 9.8. Earning more points is the only way up.

What the listings tell you

Five relay listings were read. Three state 4-pin and 5-pin fit, two show a green and red LED readout, one states a warranty term, and none states a UL, ETL or CSA listing. Two listings share nearly the same description text, and one lists two different size figures.

Buying guide: your first relay tool

Pin fit

The 4-pin and 5-pin fit is the one listed here, so match the tool to the relay in the fuse box. Three of the five tools here list 4-pin and 5-pin fit, and two of those detect the pin layout on their own. The bypass kit plugs into the relay position instead, so pin count matters less there.

Voltage range

A car battery is 12V, and the two Sound Troubleshooting units list an 11V to 15V working range with a coil resistance above 20 ohms preferred. The KONNWEI KW371 adds 6V and 24V coverage for motorcycles, cars, trucks and boats, while the Innova 5420 applies 3V, 5V, 12V or 24V to the circuit under check.

Readouts

A green light means the relay is good and a red light means it is bad on the two Sound Troubleshooting units, which is the simplest readout here. The KONNWEI KW371 shows a graphical waveform display, and the Innova 5420 shows voltage on a 1.25 in backlit LCD with LED polarity indicators. The bypass kit has no readout at all: it gives direct control of the circuit instead.

Bypass kit or dedicated unit

A bypass kit plugs into the relay position and lets the circuit run, which points at a bad relay when the component works with the bypass in place. A dedicated unit runs the relay through several cycles and reports the result, which suits a check of a relay already pulled from the car. Pick the bypass kit when the fault is still in the car, and a dedicated unit when the relay is already in hand.

Garage Fit Check

• Power comes from the car battery on the clip-on tools: the two Sound Troubleshooting units clip to the battery, and the KONNWEI KW371 runs from the vehicle battery with no separate batteries needed.
• The RVMARINEPAT kit is a 6-pack, so it needs more drawer space than a single handheld unit.
• The Innova 5420 ships with a 20 ft cable, the longest lead stated here.
• Check pin fit before the first job: three of the five list 4-pin and 5-pin fit, and the two Sound Troubleshooting units prefer a coil resistance above 20 ohms.

FAQ: garage tools

How does a relay tool show a bad relay?

On the two Sound Troubleshooting units, a green LED means the relay is good and a red LED means it is bad. The unit detects the pin position and runs the relay through several cycles before it lights the result.

What pin counts do these relay tools fit?

Three of the five list 4-pin and 5-pin fit: the KONNWEI KW371 and the two Sound Troubleshooting units. The Innova 5420 and the RVMARINEPAT bypass kit state no pin fit.

Can one tool check both a battery and a relay?

Yes. The KONNWEI KW371 is a 2-in-1 battery and relay tool: it runs battery health, cranking and charging checks with a 10 to 2000 CCA range and a 5 to 220 Ah range, and it diagnoses 4-pin and 5-pin relays.

What is a relay bypass kit for?

A bypass kit plugs into the relay position and gives direct control of the circuit, so a fuel pump, window motor or headlight can run while the relay is out of the loop. The RVMARINEPAT 6-pack replaces 9036 and 9037 and covers 20 amp continuous and 30 amp surge at 12V.

Do I need a 24V relay tool for a car?

No. A car battery is 12V, and the two Sound Troubleshooting units are built around that. The 24V coverage on the KONNWEI KW371 and the Innova 5420 suits trucks and boats, which the KW371 listing names.

Related: the best automotive relay box kit, the best automotive multimeter under 40, the best battery tester for AGM batteries, the best high amp automotive relay and the best automotive fuse kit under 10.