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Home / Lighting / Driving & light bars

Britax RM4-2435R micro-ISO relay — 24V 35A resistor-protected 4-pin, black plastic housing (alt written from product data, not visually confirmed)Britax RM4-2435R pin assignment diagram — 4-pin micro-ISO relay showing coil pins 85 and 86, battery feed pin 30, switched output pin 87

Britax

Micro Relay — RM4-2435R 35A 24V 4-Pin N/O Resistor

RM4-2435R

24V 35A single-contact micro-ISO relay with resistor coil protection. Switches lights, horns, compressors and pumps on trucks, buses, agricultural and 24V marine systems. Plugs into any micro-ISO 4-pin base.

35A · 24V DC
4-pin micro-ISO
Resistor coil protection

$15.00

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Universal fitment24V systems only — micro-ISO 4-pin base

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A micro-ISO relay that switches up to 35A on a 24V circuit through a single normally-open contact. Runs truck driving lights, auxiliary tail lights, horn circuits, compressor coils and air-horn triggers off the one relay. Fits truck fuse-box bays, bus auxiliary panels, agricultural harness looms and 24V marine distribution boards.

The 15×15×22mm body plugs into a standard micro-ISO 4-pin base (same 2.8mm blade pattern as every other brand's micro relay). Pin 85 and 86 drive the coil, pin 30 carries battery feed, pin 87 switches the load. A resistor sits across the coil terminals and absorbs the voltage spike when the relay drops out, so the trigger device sees a clean turn-off instead of a kickback that fries its driver stage.

The 35A rating is the ceiling on the switched contact, not an invitation to run a winch or a large inverter through it. Winches draw 200 to 500A under load and belong on an ANL or Class T fuse with a dedicated solenoid; large inverters belong on an in-line solenoid rated for their continuous draw. Fuse the relay feed at the source with a 30A blade fuse to match the contact rating.

Pairs with

[handle:mini-relay-base-c-w-terminals-suits-4-5-pin-relays]

  • Micro-ISO footprint — plugs into any 2.8mm 4-pin micro relay base
  • 35A switched contact — handles driving lights, horns, compressors on 24V
  • Resistor coil protection — absorbs the kickback when the relay drops out
  • 24V heavy-vehicle rating — made for trucks, buses and 24V marine
  • Normally-open contact — load off until the trigger closes the coil
  • Compact 15×15×22mm body — fits where mini-ISO relays won't
  • Low 0.08A coil draw — triggerable from any ignition-sense or dash switch
  • Britax trade-brand backing — mainstream AU auto-electrical supplier

Electrical

Voltage: 24V DC

Switched current: 35A continuous

Contact: SPST N/O

Pin count: 4

Pin pattern: Micro-ISO 280 Series

Coil draw: 0.08A at 24V

Protection: Resistor across coil

Operating temperature: -40°C to +85°C

Physical

Dimensions: 15 × 15 × 22 mm

Weight: 20g

Terminals: 2.8mm blade

Housing: Polyamide (PA66)

Country of origin: China

Length: 15mm

Width: 15mm

Height: 22mm

Weight: 0.1kg

24V systems only — micro-ISO 4-pin base
24V heavy vehicles, trucks, buses, agricultural, 24V marine
Not compatible with 12V systems — the 24V coil won't pull in at 12V
Not for mains-voltage AC switching
Not for loads above 35A — use a Britax R4-1280R 80A heavy-duty mini relay for larger loads

Q: What does "micro-ISO" actually mean?
It's the smaller of the two standard automotive relay footprints. Micro relays use a 4-pin or 5-pin pattern on 2.8mm blade terminals and sit on a 15mm square footprint. Mini relays use the same pin layout but on 6.3mm blades and a 26mm footprint. Any micro-ISO relay plugs into any brand's micro-ISO base.

Q: What does "35A N/O" mean on this relay?
35A is the continuous current the switched contact can carry. N/O means normally open — the contact is open (load off) until the coil energises and pulls it closed. A normally-closed relay works the opposite way, which suits safety circuits that need to lose power when a trigger activates.

Q: Why does it need resistor protection?
When you cut power to a relay coil, the collapsing magnetic field pushes a reverse-voltage spike back down the trigger wire. The spike can reach a few hundred volts for a few microseconds — enough to blow the driver stage of a solid-state switch, a BCM output or an LED controller. The resistor across the coil terminals burns the spike off as heat instead of letting it exit the coil.

Q: Will this work with 12V trigger systems?
No. A 24V-coil relay won't pull in at 12V — the magnetic force is too weak. For a 12V truck or 4WD, use a 12V-rated micro relay instead.

Q: What size cable and fuse do I run on the switched side?
Match the fuse to the load, up to the relay's 35A ceiling. Use 4mm² automotive cable (rated around 30A continuous) for loads up to 30A and run a 30A blade fuse at the battery end of the feed wire. Loads above 30A want 6mm² cable (around 45A) and a 35A fuse.

Q: Can I run a 24V winch through this?
No. Winches draw 200-500A under load, far beyond this relay's 35A ceiling. Winches need a dedicated contactor-style solenoid rated 300-500A, protected by an ANL or Class T fuse. This relay is for lights, horns, pumps and compressors in the 5-30A band.

Q: Where does the resistor sit — I don't see it?
It's internal, bonded across pins 85 and 86 inside the plastic case. A multimeter in resistance mode across the coil terminals reads a few hundred ohms instead of around 90 ohms of an unprotected 24V coil — that's the resistor in parallel.

Q: Does the base matter — can I use a 12V micro relay base?
The base is 12V/24V neutral. The relay carries the voltage rating; the base just distributes current. Any micro-ISO 4-pin base takes this relay.

Q: Can it mount upside-down or sideways?
Yes. The contacts are gravity-neutral and the relay works in any orientation. Mount it to put the terminals in reach for troubleshooting; orientation doesn't affect switching reliability.

Q: What's the coil draw — can I trigger it from an ignition-sense wire?
Around 80mA at 24V. That's within the budget of any ignition-sense wire or a dash switch, so no slave relay is needed on the trigger side.

Q: How does it compare to the 12V version of the same relay?
Same physical body, same pin pattern, same contact rating. The only difference is the coil winding, wound for 24V on this part. Trucks and buses go on 24V; 4WDs, utes and caravans go on 12V. Order the voltage that matches the vehicle's own system, not the load.

Q: What warranty is on this?
12 months against manufacturing defects — the Britax commodity-tier default. Covers coil failure, contact welding, cracked plastic housing and dead-on-arrival parts, provided the relay was wired and fused within its 35A ceiling and installed in the right voltage system. Over-current, reverse polarity, short-circuit faults in the surrounding harness, and water ingress on a non-sealed relay are owner-side.

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