Hydraulic Solenoid Valve Connectors: Comparing 5 Wiring Types, IP Ratings and Selection Criteria

The connector is the electrical interface between your control signal and the solenoid coil.The same valve installed on an outdoor mobile machine and in a dry cleanroom production line requires two very different connector solutions. This guide compares the five connector types offered by Tai-Huei — LW Terminal Box, DL DIN Plug, M4 Pin Type Fast Connector, 2W Two Wires and DT Deutsch Connector — by ingress protection rating, mounting method and operating environment, so you can match the wiring solution to the conditions your equipment actually sees.

In practice, the reliability of a solenoid directional valve depends on far more than the machining accuracy of the valve body. The choice of connector is often what determines whether a machine runs continuously for years or trips a production line. Where the connector design or IP rating does not match site conditions, coolant ingress, metallic dust build-up and vibration-induced loose contacts follow — and an entire automated line can be forced to stop.

Tai-Huei has more than 50 years of experience developing and manufacturing hydraulic valves.Our G02/D03 (1/4" / NG6) and G03/D05 (3/8" / NG10) solenoid directional valve series are available with five connector types — LW, DL, DT, M4 and 2W — covering a wide range of mounting arrangements, wiring requirements and operating environments. The sections below outline the characteristics, typical applications and selection considerations for each.

Further reading: How to Select Hydraulic Solenoid Valve Size: Flow Rating Chart and ISO 4401 Mounting Interfaces

The five Tai-Huei connector types

Five standard wiring types are available, each suited to a different combination of environment and installation constraint.

DL — DIN Plug Type

The DL connector conforms to the DIN 43650 Form A standard and incorporates an LED that indicates coil energization in real time. A screw-retained design gives a secure mount with straightforward installation and removal, and the assembly achieves IP65 protection.

Technical features.

When the coil is energized, the integrated LED illuminates. Maintenance staff can confirm at a glance whether the coil has received its control signal. When a fault occurs there is no need to reach for a multimeter first — the indicator alone shows whether the control signal from the PLC is present, which cuts fault-finding time considerably.

Pin assignment.

The standard configuration is a 3-pin connector. Pins 1 and 2 are the supply terminals (AC coils are normally non-polarized; DC coils must be wired to the correct polarity). Pin 3, or a separate terminal, is the protective earth (PE) connection.

Points to note.

DL connectors use different indicator circuits for AC and DC coils. AC versions normally include a rectifier, while DC versions require attention to polarity and to the orientation of any protective components such as flyback diodes. Specifying the wrong version, or wiring it incorrectly, may prevent the LED from illuminating or damage the indicator circuit. Confirm coil voltage, supply type (AC or DC) and connector specification before ordering.

LW — Terminal Box Type

The LW connector uses a dedicated terminal box with internal terminal-block wiring and a built-in surge suppressor. The generous internal volume accepts larger cable cross-sections and improves both wiring convenience and electrical protection.

Technical features.

The box provides ample room to work, accommodating heavier-gauge cable terminated on screw terminals. The result is a secure, maintainable connection well suited to large conductor sizes and long cable runs.

Circuit protection.

De-energizing a solenoid coil generates a reverse voltage transient. The varistor installed inside the terminal box absorbs this surge, reducing stress on PLC output modules, relays and other control components, and extending the service life of the control system.

M4 — M12-4Pin Type Fast Connector (M12-4PIN)

The M4 connector uses a standard M12 4-pin circular format, combining the control signals for both coils of a double-solenoid valve into a single outlet. A metal threaded coupling provides good sealing, vibration resistance and connection stability. Once the machine is wired, servicing requires no re-stripping of conductors or disturbing of terminals — the connector simply unscrews, allowing a rapid valve change with far less risk of wiring error.

Technical features.

The standard M12 4-pin format is keyed against mis-mating and accepts off-the-shelf M12 cordsets, so no field crimping or rewiring is required.

Pin assignment.

Pin 1 — common (COM).

Pin 2 — solenoid A control signal.

Pin 3 — reserved (not used)

Pin 4 — solenoid B control signal.

Application advantages.

The connector interfaces directly with PLCs, distributed I/O modules and IO-Link systems, reducing field wiring complexity and supporting a more modular machine architecture.

2W — Two Wires Type

The 2W connector uses a high-protection direct-exit design: two insulated conductors emerge from the coil body itself, potted in a single high-temperature resin molding. Eliminating the external plug and terminal box saves installation space. The assembly achieves IP67, giving effective protection against dust ingress and temporary immersion.

Technical features.

Because the conductors and coil are potted as one piece and sealed at the exit point, the number of external connectors and contact points is reduced — lowering the risk of failure from moisture, oil contamination or intermittent contact, while saving space.

Application advantages.

Well suited to hydraulic power units (HPUs), control cabinets and other space-constrained installations. The leads can run straight to a terminal strip inside the cabinet, reducing the number of wiring interfaces and improving overall reliability.

DT — Deutsch Connector Type

The DT connector uses the Deutsch DT04-2P format, with twin-rail contact design, a high-density O-ring, sealing gaskets and a rubber boot for excellent sealing, weather resistance and vibration tolerance. A latching quick-connect design allows fast installation and removal, and the assembly achieves IP68.

Technical features.

Multiple sealing barriers keep out moisture, oil and dust, reducing contact oxidation and intermittent connection. Electrical performance remains stable even under prolonged outdoor exposure or regular high-pressure washdown.

Application advantages.

The IP68 rating improves reliability where mud, spray, humidity and dust are present, reducing the risk of contact oxidation and signal faults caused by water ingress and contamination. The latching mechanism also reduces the chance of the connector working loose under vibration.

Click to View Tai-Huei Hydraulic Solenoid Valve Coil Protection Rating Test Reports

Further reading: Why Hydraulic Solenoid Valve Coils Overheat and Burn Out: Causes, Prevention and Selection Guide

Application guidance and connector selection

Start by assessing the operating environment, then select the corresponding IP rating and connector format.

DL DIN Plug Type (IP65)

Suitable for general industrial environments, the built-in LED provides a visual indication of coil energization, enabling quick verification of the control signal and reducing troubleshooting time. Ideal for machine tools, automation equipment, and injection molding machines.

LW Terminal Box Type

Ideal for heavy machinery, medium and large scale hydraulic systems, and equipment requiring continuous operation. The junction box design offers flexible wiring, easy maintenance, and ample internal space for future wiring modifications or the installation of protective devices such as surge suppressors.

M4 M12-4Pin Type Fast Connector (M12-4PIN)

Suitable for automated production lines requiring frequent maintenance, tool changes, or valve replacement. The threaded coupling nut allows quick installation and removal, enabling valve replacement within seconds. It integrates seamlessly with distributed I/O and IO-Link systems, making it ideal for semiconductor equipment, automated material handling systems, and lithium battery manufacturing lines.

2W Two Wires Type (IP67)

Suitable for densely arranged valve assemblies and space-constrained installations, including hydraulic power units, compact control cabinets, and outdoor equipment. The 2W connector is an excellent choice for applications requiring long-term operation in damp, dusty, or high-vibration environments where simplified wiring and compact installation are essential.

DT Deutsch Connector Type(IP68)

Designed for demanding outdoor applications involving high humidity, heavy vibration, mud, and water spray, the DT connector is widely used in construction machinery, excavators, port cranes, agricultural machinery, and vehicle-mounted hydraulic systems. Its advanced sealing performance and excellent vibration resistance help minimize the risk of contact oxidation, intermittent connections, wiring failures, and signal interruptions caused by harsh operating conditions.

Choosing the right connector for your machine

No connector type is inherently better than another. What matters is the fit with your equipment, operating environment and maintenance strategy.

Step 1 — Define the operating environment.

Establish whether the equipment runs indoors or outdoors, and whether moisture, oil, dust, coolant or heavy vibration are present.

Step 2 — Select the IP rating.

Determine the dust and water protection the site actually requires, and set the IP rating accordingly.

Step 3 — Assess maintenance frequency.

Consider your maintenance and replacement requirements, and whether quick-disconnect, energization indication or other maintenance-oriented features are worth having.

Step 4 — Confirm wiring and installation space.

Finally, review the control cabinet, manifold and surrounding clearances, and choose the connector that best matches your wiring method and mounting constraints.

If you are unsure which connector is best suited for your installation, contact the Tai-Huei engineering team directly.

Connector selection — frequently asked questions

Q: Why do connector type and IP rating have such a direct effect on machine reliability?

The solenoid directional valve is a key control component in a hydraulic system, directing oil flow to actuate cylinders and motors. Industrial environments can expose connectors to coolant mist, water vapor, oil, dust, and metal particles. If the connector's IP rating is not adequate for the operating environment, moisture and contaminants can penetrate the connector and reach the electrical contacts, causing corrosion, increased contact resistance, intermittent connections, or, in severe cases, a short circuit that damages the coil. Selecting the right connector helps reduce the risk of electrical faults and unplanned downtime.

Q: Is there a real case where the wrong connector caused a line stoppage?

Yes. A major Taiwanese machine tool manufacturer relocated a hydraulic valve manifold beneath the machining tank as part of a customer-driven design change. The new location exposed the valve assembly to heavy coolant spray. The machine was equipped with DL DIN Plug Type connectors (IP65). Although IP65 provides protection against dust and low-pressure water jets, the connectors were subjected to prolonged exposure to concentrated coolant and moisture. Within six months, water ingress caused repeated electrical faults, preventing the solenoid coils from actuating reliably. The problem was initially suspected to be valve spool contamination, and several valves were replaced without resolving the issue.

After a Tai-Huei engineer inspected the equipment on site, the root cause was identified as insufficient ingress protection for the installation environment. Based on our recommendation, the connectors were replaced with DT Deutsch Connector Type connectors with IP68 protection. Since the changeover, the same valves have continued to operate reliably in the same demanding coolant environment, with no further stoppages caused by water ingress.

Q: How does water resistance differ between the DL, 2W and DT connectors?

The main differences are their IP ratings and sealing designs. The DL DIN Plug Type (IP65) provides protection against dust and low-pressure water jets and includes a built-in LED for visual confirmation of coil energization. The 2W Two Wires Type (IP67) uses a molded two-wire lead design in which the conductors are integrated with the coil, reducing external connection points and the potential for water ingress. The DT Deutsch Connector Type (IP68) provides a higher level of protection against water ingress and is designed for demanding environments requiring strong sealing and vibration resistance.

Q: Why are more smart automation builders specifying the M4 Pin Type Fast Connector (M12-4PIN)?

The M12 4-pin interface is widely used in industrial automation and modular machine architectures because it provides keyed mating, quick connection and disconnection, and reliable mechanical retention.

With conventional wiring, replacing a valve may require disconnecting individual wires, removing terminals, and reconnecting them according to the wiring diagram. This takes time and creates opportunities for wiring errors. With the M4 connector, the valve can be replaced by simply loosening the threaded coupling nut, disconnecting the connector, installing the replacement valve, and reconnecting it. This can significantly reduce replacement time and simplify maintenance. The connector can also interface with distributed I/O systems, making it well suited to modular machine designs and automated production lines.

Q: Which connector is recommended when manifold space is tight?

The 2W Two Wires Type connector is a strong choice for space-constrained installations. Unlike the DL and LW types, which require an external connector body or terminal box, the 2W uses two leads that exit directly from the coil, eliminating protruding connector hardware and reducing interference with adjacent components. This makes it particularly suitable for hydraulic power units (HPUs), compact control cabinets, and densely arranged valve manifolds. Its IP67 protection also provides effective protection against dust and water ingress in damp or dusty environments.

Q: Is IP68 always better than IP67?

Not necessarily. IP68 offers a higher level of dust and water protection, but IP67 is often sufficient in ordinary damp environments. Select the rating according to the actual operating conditions rather than always specifying the highest one. An IP rating also describes only resistance to water and dust — it does not prevent a coil from burning out because of abnormal voltage or overheating.

Connector selection is about lifecycle cost, not unit price

When designing a machine, connector cost may appear to be a relatively small part of the overall equipment cost. For industrial equipment operating continuously, however, maintenance time, unplanned downtime, and troubleshooting efficiency can have a much greater impact on total cost of ownership (TCO).

For example, automated equipment that requires frequent tool changes, valve replacement, or rapid servicing can benefit from the quick-disconnect design of the M4 M12-4Pin Type Fast Connector or DT Deutsch Connector Type. These connectors can reduce replacement time and eliminate many of the wiring errors associated with disconnecting and reconnecting individual conductors. The LW Terminal Box Type is better suited to fixed installations where wiring flexibility and easy access to internal terminals are important, while the DL DIN Plug Type is a practical choice when visual confirmation of coil energization is useful.

Connector selection should therefore be based on more than purchase price. Operating environment, required ingress protection, maintenance frequency, installation space, and the potential cost of downtime should all be considered. Where an equipment stoppage is costly, investing in a connector that reduces maintenance time and the risk of electrical faults can provide a better return over the equipment's service life.

Written by the Hydraulic Systems Application Engineering Team, Tai-Huei Hydraulic. Last updated: July 2026.

References and Applicable Standards

The connector types and protection rating definitions described in this article are based on the following international standards. Actual product specifications shall be subject to Tai-Huei Hydraulic product catalogs and test reports.

IEC 60529 — Degrees of protection provided by enclosures (IP Code), Edition 2.2 (2013)
The definitions of IP65, IP67, and IP68 in this article are based on this standard. The first digit indicates protection against solid particles (dust), and the second digit indicates protection against water ingress.

DIN EN 175301-803 — Rectangular connectors for solenoid valves (formerly DIN 43650)
Form A connectors feature an 18 mm pin spacing. The DL LED indicator connector described in this article complies with this specification.

IEC 61076-2-101 — Circular connectors, M12 threaded locking connectors
The M4 (M12 4-Pin) quick connector described in this article is based on this standard.

TAI-HUEI Hydraulic Industry Co., Ltd. solenoid valve coil protection rating test reports and product catalogs.

Verification Date: July 28, 2026
Standards and specifications are subject to revision. In case of updates, the latest information published by the issuing organizations shall prevail.