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Small black rectangular relay with four metal terminals and 12 30 40 labels

METRA

METRA RL3040 Install Bay Economy Relay 12V 30/40A car electronics accessory

SKU CH-KJWT-BFDN4

Economy 12 V relay rated at 30/40 A for lighting, alarm and stereo circuits

  • Product typeCar Stereo Add-Ons
  • 12 V relay handles 30 A and 40 A loads
  • Suits HID and fog-light installations
  • Works with car alarms and remote starts
  • Fits any radio or stereo upgrade

Install Bay Economy Relay 12V 30/40A

The METRA RL3040 is a 12 volt automotive relay rated at 30 and 40 amps. It is designed for car stereo add-ons and general 12V switching tasks. Installers use it to control higher-current accessories from a low-current trigger wire.

HID, fog light, alarm and remote start upgrades

This relay replaces a missing or undersized factory relay when adding HID lighting, fog lights, car alarms or remote start systems. The jump is worth it when the new accessory draws more current than the original circuit can safely switch. Buyers needing multiple isolated circuits or a different pin layout will need additional relays.

How it compares

Measured against everything we stock in Car Audio Accessories & Wiring, at today’s prices. Recalculated every night.

Price $4.99
Cheaper than about 96% of the 2,768 comparable items (median $21.99).

Specifications

Product
Product typeCar Stereo Add-Ons

Questions about this item

What socket size does the RL3040 relay need to plug into?

The RL3040 uses a standard ISO micro relay footprint with four pins, so it plugs directly into a matching four-pin socket or relay block.

Which step do installers most often miss when wiring this relay?

They frequently forget to fuse the 30/40 A power feed at the battery, leaving the high-current circuit unprotected.

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