Trailer Light Issue/Question

[BMWtoF150]

I have a 2021 3.5eco Max Tow and also a utility trailer used to haul brush, law mower, etc.

When I attach my trailer to my truck using a B&W three ball hitch the lights will not work and the truck does not detect the trailer.

if I attach the trailer to the truck using a standard Reese hitch everything works correctly.

Any idea what would cause this?

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[Buyer2021]

Any idea what would cause this?

A poltergeist

Seriously, there's no 'connection' between the drawbar / ball and the trailer detection / lights operation.

I suspect that something about the B&W physical setup is causing your trailer umbilical-cord connection to be displaced slightly, causing it to not make a good connection in your bumper socket.

Long shot - if the ground circuit through your umbilical connection is not complete, the Reese may be completing that circuit while the B&W is not for some reason (e.g. good paint coating). Your trailer should not be dependent on completing the ground circuit through the ball, that should be a circuit via the umbilical connection.

Check the integrity / continuity of your umbilical ground circuit (your trailer should be detected and its lights work when plugged into the truck-socket without being hitched or having any contact at the ball).

With your trailer plugged-in but not in contact with the ball, you should have continuity (use a multimeter set to Ohms) between a bare-metal spot on the truck chassis and a bare-metal spot on the trailer chassis. If you don't, your umbilical ground circuit is broken - then you've got to track down where that break is located. Wiggle your trailer plug in the truck socket while doing this test to see if there's intermittent loss of contact there.

Good Luck!

 

[Kanuck]

On a 4 pin connector the white is the ground. Make sure it has a good, clean connection to the trailer frame.

 

[Fomoco65]

Change your trailer to a 7 pin connector with a direct ground on trailer .

 

[powerboatr]

Ditto
It's 99% a ground issue
Good solid frame to pigtail ground
Is required...

 

[Buyer2021]

Change your trailer to a 7 pin connector with a direct ground on trailer .

A 4-pin connector has a circuit for ground just like a 7-pin connector, there's no benefit in changing the trailer connector type, just get the one they have working properly.

 

[jhelrey]

I convert all of my trailers over to 7 way because it's less finicky.

 

[Buyer2021]

I convert all of my trailers over to 7 way because it's less finicky.

Many RV owners would dispute that. Threads about lighting issues that ultimately prove to be due to 7-way connector problems are pervasive on RV forums.

The flat-blade 7-way connectors are much more sensitive to the quality of the plug & socket (there's lots of really crappy versions on the market), whether the blade clamps are single or double-sided, the robustness of the spring steel used, etc.

By comparison the common 4-pin SAE-type connector is a long-proven robust and trouble-free connector IME.

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