DC 12V 40A Automotive Relay SPDT 4-Pin | Car Alarm & Circuits
DC 12V 40A Automotive Relay SPDT 4-Pin | Car Alarm & Circuits
DC 12V 40A SPDT Automotive Relay – 4-Pin High-Load Car Relay
Keep your vehicle's electrical systems running reliably with this heavy-duty DC 12V 40A SPDT Automotive Relay. Built for high-load switching applications, this 4-pin (also available in 5-pin) relay is an ideal component for car alarm systems, lighting circuits, starter circuits, and a wide range of 12V automotive wiring projects. Its single-pole double-throw (SPDT) design provides one normally open (NO) and one normally closed (NC) contact, giving you flexible switching control in a compact, durable package.
Key Features
- High Current Rating: Handles up to 40 amps, making it suitable for high-load automotive circuits
- SPDT Configuration: 1 Normally Open (NO) + 1 Normally Closed (NC) contact for versatile switching
- 12V DC Coil Voltage: Designed specifically for standard 12V automotive electrical systems
- 4 or 5 Pin Options: Compatible with a variety of relay sockets and wiring harnesses
- Durable Construction: Sturdy plastic housing with metal contacts for long-lasting performance
- Wide Application: Suitable for car alarms, horns, headlights, cooling fans, starters, and more
- Low Voltage Compliant: Rated for low-voltage use (below 50V AC or 75V DC) per EU LVD standards
- Compact Black Design: Discreet, easy-to-mount black housing fits standard relay locations
Specifications
| Coil Voltage | DC 12V |
| Current Capacity | 40A |
| Contact Type | SPDT (1 NO + 1 NC) |
| Pin Configuration | 4 or 5 Pins |
| Construction | Plastic housing, Metal contacts |
| Color | Black |
| Voltage Standard | Low Voltage (Below 50V AC / 75V DC) |
| Country of Origin | Made in China |
What's in the Box
- 1 × DC 12V 40A SPDT Automotive Relay
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Frequently Asked Questions
Q: What is an SPDT relay and how does it work in a car alarm system?
A: An SPDT (Single-Pole Double-Throw) relay has one common terminal and two switching contacts — Normally Open (NO) and Normally Closed (NC). In a car alarm system, the relay acts as an electrically controlled switch: when the alarm coil is energized with 12V DC, the common terminal switches from the NC contact to the NO contact, allowing you to trigger horns, sirens, or cut ignition circuits without running high-current wires through delicate alarm modules.
Q: Can this relay handle accessories like headlights, cooling fans, or horns?
A: Yes. With a 40-amp current capacity and a 12V DC coil rating, this relay is well-suited to switch high-draw automotive accessories including headlights, electric cooling fans, horns, and starter circuits. Always verify your accessory's peak current draw does not exceed 40A before installation.
Q: Is this relay compatible with standard relay sockets?
A: This relay features a 4-pin or 5-pin configuration that fits most standard automotive relay sockets and wiring harnesses available on the market. Check your socket's pin layout (typically labelled 85, 86, 87, 30, and optionally 87a) to confirm compatibility before installation.
Q: Does this relay require any special tools to install?
A: No special tools are required. The relay plugs directly into a compatible relay socket. For direct wiring, basic automotive wiring tools such as a wire stripper, crimper, and a screwdriver are sufficient. Always disconnect the vehicle battery before working on electrical circuits.