Trailer Lights Gurus--Got a Question.

[mbsimpson99]

With a 4pin connector the taillights and signal lines are only energized when the vehicle's are.

Whatever the vehicle behavior is will be what your lights are: so if your vehicle has no markers unless the headlights are on, the same goes for the trailer

I agree this is how they should work. I had a similar issue on my Ford Excursion. I had turn signals but no taillights. Only had 8-9 volts at connector. Checked ground, jumpered a temporary ground still no luck. Fuses checked good. Found a fuse for trailer tow relay. It checked good but in the process of removing and replacing fuse the connector read 12 volts. Couldn’t get it to stay on but looks like it is due to bad contact in the fuse holder. The 7 blade connector reads good so I am going to swap in a new 7 blade with a 4 blade built into it. Hopefully that will bypass the bad 4 pin wiring.

 

[Dmacleo]

So, I'm curious why npalen needs his trailer lights on without his tow vehicle lights on.

yeah I missed a lot in this long thread but iirc NO lights (brake/turn) worked w/o the light switch being on.

in the many pages I did not see vehicle make/model.
from approx 2008 on gmc truck trailer lights controlled by a Trailer Lamp Control Module usually mounted by spare tire. if it does not have that all triler lighting controlled by the body control module.
many fords control this off the LCM (light control module) for my 2010 marquis had to buy a Circuit Protected ModuLite such as this:

https://www.etrailer.com/Wiring/Mercury/Grand+Marquis/2010/119179KIT.html?VehicleID=20101174601

places like etrailer have kits for this.
my kit (can't find link for) kit required a circuit breaker protected power (linked one is a 10A fuse is updated version of what I got) off battery, that provides power to the lights depending on what the LCM sends out as signal.
I then plugged the 4 pin output into this:

https://www.etrailer.com/Wiring/Tow_Ready/30717.html

to give me 7 pin which I then wired trailer brake module (aftermarket) into as well as full time power for breakaway battery charging and I also hooked relay up to my reverse light (rev light only used as signal) and used those incoming 40A wires to power reverse light under bumper as well as 4 led reverse lights on trailer.

point I am trying to make is you can no longer just splice the 4 wires onto the wires at tail light end.

 

[WranglerX]

Many Fords do not have a flasher unit. My '08 F350 turn signals are controlled by the ECM. Found that out when I went to install LED's. Have to use external resistors on all four corners, but that also compensates for LED trailer lights.

Yes!...

 

[npalen]

Do brake lights still work with ignition off?

Bruce

Bruce--I think I checked that and they do work but will double check.

 

[bigwave]

Hi NPALEN, back at entry number 76 you posted a picture of wiring that I presume came from ad, look at bottom example where it shows 3 wires coming out of fixture, if fixture only has 2 wires it doesn't have both tail & brake / turn light functions, they either gave you a bad set of fixtures or you got ONLY tail or brake / turn function fixtures; not both. the 2 wires; either brown / yellow or brown / green coming back can't be hooked together. if you can open fixture look and see if there's a third wire maybe tucked inside. There are dim and bright LED's for the 2 functions. Hope this helps,

 

[Doughknob]

Who is his grampa?

He IS?

 

[npalen]

He IS?

Oh, I get it. His Grampa is He. I suppose He has a brother named Haw. (Who would perhaps be a great uncle to Who)

 

[NCL4701]

Apologize if this has been said as I haven’t read every word of this thread.

I have a friend with a late model Jeep Cherokee he uses to tow a boat trailer with a 5 pin flat plug. He had the exact same problem. We hooked it to my Tundra and the trailer lights worked normally. He contacted the dealership and they told him that’s how the lights work on his Jeep. Never heard of such but now he just knows he has to turn on at least the parking lights whenever he’s towing.

 

[ForestGrump]

Normally trailer lights are connected to the vehicle lights. How else would your turn signals and brake lights work?

 

[CausticUrbanCoast]

Normally trailer lights are connected to the vehicle lights. How else would your turn signals and brake lights work?

Depends if your vehicle has a towing package or not, if so they may not be tapped into the lighting harness.