Creltek 3-Line Trailer Light Converter

What is it?

This is a power module designed to control trailer lights based on signals from your vehicle's lighting circuits. Most vehicles have at least 4 separate circuits: Running (Tail) Lights, Brake, Left Turn, and Right Turn. Most basic trailers have a 4-wire connector with only 3 signals: Running (Tail) Lights, Left Turn, and Right Turn. The trailer does not have a separate circuit for Brake lights; applying the Brake is supposed to light up both the Left and Right Turn signals together.

This module combines the Brake and Left and Right Turn signals in an intelligent way, and also isolates the electrical load of the trailer lights from the vehicle's own lighting circuits.

Why did you make it?

After installing a towing hitch on my own vehicle, I needed to install wiring for the trailer lights. There are a couple usual approaches to doing this, neither of which really appealed to me:

• Wire the vehicle's Brake signal into each of the Trailer's Turn signals with 4 large diodes. There are two downsides to this: The diodes can dissipate a significant amount of heat (up to several Watts each!), and if the Brake is held on while a Turn signal is active, the trailer's Turn/Brake signal lamp is lit continuously, which obscures the fact that your Turn signal is flashing.
• Purchase an aftermarket wiring kit. Some of these are really just a dumb set of packaged diodes, with the problems listed above. Others incorporate mechanical relays (which can noisy and prone to mechanical failure). Others appear to use some sort of transistor output, but they seemed to be rather expensive.

Of course the logical thing to do was build it myself, to my own specifications. :)

What makes it special?

This lighting controller uses XOR gates to intelligently combine the Brake and Turn signals. If the Brake is applied, both of the trailer's Left and Right Turn signals are lit; however, if the vehicle's Left Turn signal blinks on with the Brake applied, the trailer's Left Turn Signal goes out. (The Right Turn signal works the same way). Without the Brake applied, the vehicle's Turn Signals blink the trailer's Turn Signals normally. In this way, the "blinking" of a Turn Signal is always visible on the trailer, even when the brake is being applied. This also seems to be the method used by the "best" aftermarket trailer light converters.

Features:

• Turn and Brake signals are intelligently combined
• Independent, rugged, high-power MOSFET Outputs for all 3 trailer lighting circuits
• High-impedance inputs sense your vehicle's lighting circuits without electrically loading them
• Trailer lighting problems or electrical shorts will not affect your vehicle's lighting circuits
• Trailer lighting can be protected with a single fuse
• Automatic power-off eliminates parasitic drain of your vehicle's battery when not in use
• On-board blue LED indicates power-on state
• Auxiliary +5VDC output can be used to optionally power other devices when active (500 mA max)
• Mounting holes for M3 screws and standoffs

Specifications:

• Designed for 12V, Negative Ground vehicle systems
• Nominal Operating Voltage: 8V to 17V DC
• Designed to withstand voltage transients up to 20V peak
• Automatic power-off timeout: Approx. 30 seconds after all lighting signals off
• Power-off parasitic current draw: less than 0.1 µA
• On-state quiescent current draw: 6-10 mA
• Input impedance: 14 kΩ
• Input current draw: less than 1 mA typical
• Input sense range: < 7.5V = Off, > 8.2V = On (18V input maximum)
• Output impedance (Signal on): 7 mΩ typical
• Designed to provide at least 5 A on each output circuit (10 A maximum)
• Outputs based on Infineon IPD068P03L3G P-Channel MOSFETs (30V, 70A, 6.8mΩ Rds on)

See Datasheet link on right for a complete schematic.

Input Terminals:

• Gnd: Vehicle Ground - connect to vehicle frame or negative (-) battery terminal
• T: Tail Light Sense - connect to vehicle positive (+) lead for Tail lights
• R: Right Turn Sense - connect to vehicle positive (+) lead for Right Turn signal
• B: Brake Sense - connect to vehicle positive (+) lead for Brake lights
• L: Left Turn Sense - connect to vehicle positive (+) lead for Left Turn signal
• +: 12V Vehicle Power - connect to positive (+) battery terminal

Output Terminals:

• +: +12V Power Pass-Thru (always on!) - optional: can be used to provide power to 12V accessories (10A max)
• T: Tail Light Output - connect to trailer positive (+) lead for Tail lights (often a Brown wire)
• R: Right Turn / Brake Output - connect to trailer positive (+) lead for Right Turn signal (often a Green wire)
• L: Left Turn / Brake Output - connect to trailer positive (+) lead for Left Turn signal (often a Yellow wire)
• G: Vehicle Ground Pass-Thru - connect to trailer frame and/or negative (-) / common lead (often a White wire)
• +5: +5VDC Auxiliary Power Output (on when device active, 500 mA max) - optional

Installation Recommendations

• Determine where you intend to mount the controller board. Choose an area protected from moisture, debris, dirt, and heat. The controller board can be mounted on brass standoffs using M3 screws, or inside a custom housing.
• Make sure that the exposed pins on the bottom of the controller board DO NOT come into contact with the vehicle frame. The board must be protected from contact with anything that might cause an electrical short, including loose items in the vehicle.
• Wire up everything except the +12V input terminal. Double-check all connections before connecting battery power.
• A maximum 15 A fuse is required between the controller board the vehicle's +12V battery. Place the fuse near the battery.
• Before connecting a trailer, verify the function of the vehicle's own Brake lights, Turn lights, and Tail lights.
• With a trailer connected, verify the function of the trailer's Brake lights, Turn lights, and Tail lights.
• Check the temperature of the board after several minutes of testing. Make sure it has enough ventilation to avoid overheating.
• Trailer lighting circuits may be individually fused if you desire. 5 A fuses are recommended; 10 A maximum.

Be sure to check out our other awesome Creltek products on Tindie!

Legal Disclaimer

This device is intended for hobbyist, experimental, do-it-yourself use only. It has not been evaluated for vehicle safety or DOT requirements. BY PURCHASING THIS ITEM YOU AGREE TO ASSUME ALL RISK AND LIABILITY INVOLVING THE USE OF THIS DEVICE, AND AGREE TO HOLD HARMLESS AND INDEMNIFY THE SELLER AGAINST ALL RISKS, LIABILITIES, AND DAMAGES THAT MAY ARISE, INCLUDING, BUT NOT LIMITED TO, PROPERTY DAMAGE, LOSS OF LIFE OR PROPERTY, BOTH OF YOUR OWN OR OF ANY OTHER PARTY INVOLVED IN AN ACCIDENT INVOLVING YOUR VEHICLE. IT IS SOLELY YOUR RESPONSIBILITY TO VERIFY THE SAFE AND PROPER INSTALLATION AND FUNCTIONING OF THIS DEVICE, AS WELL AS MEETING ANY INSPECTION AND SAFETY REQUIREMENTS IN YOUR JURISDICTION. USE AT YOUR OWN RISK. THIS PRODUCT IS INTENDED FOR EXPERIMENTAL OFF-ROAD USE ONLY.