The abbreviation “TM” found on some trailer plugs, particularly those used with older European and Australian vehicles, stands for Tail Marker. It indicates the terminal connected to the vehicle’s tail marker lights, also known as parking lights or position lights. This terminal supplies power to these lights on the trailer, ensuring its visibility during low-light conditions.
Understanding Trailer Plugs: A Comprehensive Guide
Trailer plugs are essential components for safely towing trailers, allowing for the transfer of electrical signals between the towing vehicle and the trailer. These signals control various functions on the trailer, including lights, brakes, and sometimes auxiliary power. Different types of trailer plugs exist, each with its own specific configuration and purpose. Understanding the function of each pin or terminal is crucial for proper wiring and safe operation. While modern North American plugs don’t typically use the “TM” designation, understanding its historical significance and European usage is still valuable.
The Role of Tail Marker Lights
Why Tail Marker Lights Matter
Tail marker lights are a critical safety feature, particularly when towing. They outline the extremities of the trailer, making it visible to other drivers, especially at night or during inclement weather. These lights are typically illuminated whenever the vehicle’s headlights or parking lights are activated. Properly functioning tail marker lights help prevent accidents by increasing the visibility of the trailer, allowing other motorists to accurately judge its size and position on the road.
European Standards and “TM”
In many European and Australian trailer plug wiring standards, the tail marker light circuit is specifically designated with the “TM” marking on the plug or wiring diagram. This ensures that the correct wire is connected to the corresponding terminal on both the towing vehicle and the trailer. While newer standards might use different notations or pin numbering systems, understanding the “TM” designation is important when working with older vehicles or trailers that adhere to these standards.
Frequently Asked Questions (FAQs) About Trailer Plugs and “TM”
Q1: What are the different types of trailer plugs?
There are several types of trailer plugs commonly used, including the 4-way flat connector, the 5-way flat connector, the 6-way round connector, the 7-way round connector (also known as the RV blade connector), and various European standard connectors like the 7-pin DIN connector and the 13-pin connector. Each type offers a different configuration of pins to accommodate varying needs and functionalities.
Q2: What’s the difference between a 4-way and a 7-way trailer plug?
A 4-way trailer plug typically provides connections for ground, tail lights, left turn signal/brake light, and right turn signal/brake light. A 7-way trailer plug includes all the functions of the 4-way, plus connections for electric brakes, a 12V auxiliary power circuit, and a reverse light circuit. This makes the 7-way plug suitable for heavier trailers with electric brakes.
Q3: How do I know which trailer plug to use?
The type of trailer plug you need depends on the functions you require and the type of plug installed on your towing vehicle. If your trailer only requires basic lighting, a 4-way plug might suffice. However, if your trailer has electric brakes or other auxiliary functions, you’ll need a 7-way or similar plug. It’s also important to consider the compatibility of the plugs on your vehicle and trailer. Adapters are available to connect different types of plugs.
Q4: What does each pin on a 7-way trailer plug control?
While the exact pin assignments can vary slightly depending on the standard, a typical 7-way trailer plug configuration includes:
- White: Ground
- Yellow: Left Turn Signal/Brake Light
- Green: Right Turn Signal/Brake Light
- Brown: Tail Lights/Running Lights
- Blue: Electric Brakes
- Black: 12V Auxiliary Power
- Purple: Reverse Lights
Q5: What happens if my trailer lights aren’t working?
If your trailer lights are not working, there are several potential causes:
- Blown fuses: Check the fuses in both your towing vehicle and the trailer.
- Faulty wiring: Inspect the wiring for any breaks, corrosion, or loose connections.
- Bad ground: Ensure a solid ground connection between the towing vehicle and the trailer.
- Damaged trailer plug or connector: Check for corrosion or damage to the plug and connector.
- Burned-out bulbs: Replace any burned-out bulbs.
Q6: How do I test my trailer lights?
You can test your trailer lights using a trailer light tester, which plugs into the trailer connector on your towing vehicle and allows you to check each light function individually. Alternatively, you can use a multimeter to test the voltage at each pin on the trailer plug.
Q7: Can I convert a 4-way trailer plug to a 7-way trailer plug?
Yes, you can convert a 4-way trailer plug to a 7-way trailer plug, but it requires additional wiring and components. You’ll need to run wires for the electric brakes, auxiliary power, and reverse lights, and you may also need to install a brake controller in your towing vehicle. This is best left to a qualified technician.
Q8: What is a brake controller and why do I need one?
A brake controller is a device that controls the electric brakes on a trailer. It allows the driver to adjust the braking force applied to the trailer’s brakes, ensuring smooth and controlled stops. You need a brake controller if your trailer has electric brakes and your towing vehicle doesn’t have one built-in.
Q9: Where can I find a wiring diagram for my trailer plug?
Wiring diagrams for trailer plugs are readily available online. You can find diagrams on the websites of trailer manufacturers, automotive supply stores, and online forums dedicated to towing and trailering. Always refer to the specific wiring diagram for your type of trailer plug to ensure proper connections.
Q10: What is the difference between SAE and DIN standards for trailer plugs?
SAE (Society of Automotive Engineers) standards are commonly used in North America, while DIN (Deutsches Institut für Normung) standards are prevalent in Europe. These standards define the dimensions, materials, and performance requirements for various automotive components, including trailer plugs. The main difference lies in the pin configurations, connector shapes, and the functions assigned to each pin.
Q11: Is it safe to tow a trailer with faulty lights?
No, it is not safe to tow a trailer with faulty lights. Operating a vehicle with malfunctioning lights is a violation of traffic laws in most jurisdictions and significantly increases the risk of accidents. Always ensure that all trailer lights are functioning properly before towing.
Q12: Where can I find a professional to install or repair my trailer wiring?
You can find qualified technicians to install or repair your trailer wiring at local automotive repair shops, trailer dealerships, and specialized trailer repair facilities. Look for technicians with experience in trailer wiring and electrical systems. Check online reviews and ask for recommendations to find a reputable and reliable professional.
By understanding the function of each terminal in your trailer plug, including the “TM” connection for tail marker lights, you can ensure safe and reliable operation when towing. Regular maintenance and proper wiring practices are essential for preventing accidents and enjoying a trouble-free towing experience.