While this page speaks to the unique Ford Smart Trailer Tow connector, this test box should work with any tow vehicle that uses a standard 7-Way Tow Connector. 

In their late model pick-up trucks, Ford has added a Smart Trailer Tow Connector.  Very little information has been posted about this system, how it work, and what it does. 

The sum total of a description of the system is "... the Smart Trailer Tow Connector, which informs you of trailer connectivity issues, burned-out or unlit trailer lights and trailer battery problems."  That's it. 

7-Way Trailer Connector Test Box

Furthermore, I was unable to activate the Trailer Tow Blind Spot Information System (BLIS), which was disabled as soon as I plugged my trailer in. Troubleshooting this system was very difficult because you have to have a trailer in tow to activate or troubleshoot the system.  

After considerable unsuccessful on-line research (no help from Google), I started looking into trailer 7-Way test adapters and test boxes.  

I quickly decided that the inexpensive test adapters with simple LED test lights were not likely to work with the F150 Smart Tow Connector because the tow connector is looking for a reasonable load on the signal wires before it will activate.  I then looked at some of the "professional" testers, but they were quite expensive ($150 to $350) and no mention as to if they were compatible with the Ford Smart Trailer Tow Connector.  

I decided to mine the Amazon store for the parts needed to build my own test box as depicted in the photo above.  The test box monitors the five most common signal wires from the 7-Way connector, neglecting the AUX (back-up lights) center terminal because (1) most trailer don't use this wire.  The wire I selected is an 18 AWG stranded cable that comes in a 20 foot length for less than $30 (still seems too high).  The 20 foot length allows the user to plug the tester into the 7-Way connector and route the cable through the rear sliding window (if you have one) so that you can monitor the system while driving.

Key features of this test box include:

  • Illuminated rocker switches for each signal wire that allows you to connect or disconnect that circuit to evaluate how the smart connector reacts.
  • When switched on, the color coded LED on the switch illuminates when the 7-Way connector applies 12 VDC power to that wire for easy verification of the signal.
  • Each signal is terminated into a 10 ohm 20 watt resistor to simulate (to some degree) the actual load applied by a trailer.  This load is what allows the Smart Trailer Connector to detect the presence of a trailer simulated by the test box.
  • Each signal has a 2mm color coded test jack for connection to a multi-meter for precise measurements. 
  • A simple inexpensive volt meter connected to the battery charge wire to monitor the charge voltage that would be applied to the trailer battery.

The links above will open a drawing with the test box schematic diagram, parts list (all from Amazon), and drawn-to-scale layout of the cover of the test box for easy fabrication.  The total cost for this box was about $100, which seems like a lot compared to the $10-$40 simple test adapters, but is considerably less that the professional models.