No running lights on trailer

I have a 2015 DBSB with the 7 to 4 pin adapter for the trailer lights. its hit or miss on every light working. sometimes my turn signals make both lights flash like hazards now i have turn signals and break lights but no running lights. i hooked up both trailers to my dads tacoma and everthing works. i used a test light and have power to everything except the running lights. has anyone had this problem? if so what do i need to do?

 

Clean the Ball on your truck Really Good. Clean up inside Coupler on the trailer Really Good. Check the Ground for the lights on the Trailer and the Ground for the trailer lights on the truck.

 

OP, did you use the same 7 to 4 pin adapter on your pop's tacoma? If so check for corrosion in your 7 pin socket. Often times ill take my 7 to 4 pin and insert/remove it a few times before final seating to scrape off any dirt/corrosion present.

Properly wired, the trailer shouldnt even need to be hooked to the ball or be touching the truck in any way for all lights to work. Do not rely on the ball to make a good ground.

 

The Engineer in me wants to believe this statement, but 30 years working at a marina towing everything under the sun says otherwise. I've seen many properly wired truck and trailer combinations that absolutely required a good ground through the trailer ball. Why? I have absolutely no idea. Trailer light (and brake) wiring is sometimes just possessed - usually on the ground side.

BTW, I too plug and unplug my trailer converter harness several times if I haven't used it in a while. I also Fluid Film the trailer connections on my 4Runner before winter every year.

 

Possessed ground, absolutely. I done seen the beyond absurd because of bad grounds.

One pickle factory machine tail light was giving me fits, until I ran wires directly from the negative battery post to the tail lights.

 

When using the test light, where are grounding the light?
There’s a few thing here that need addressed/answered.

Do the running lights NEVER work?
Are you using the same 7-4 pin adapter on your dads truck?
Have you used the test light to check the ground pin?

Not that it matters at this point, but I bought a 7-4 pin with “test” lights built in.
It helps narrow down, truck or trailer issues.
Similar to the one linked below. (I think mine is a Curt brand)

$10 Hopkins 47345 4 Wire Flat Adapter

https://www.amazon.com/Hopkins-47345-Wire-Flat-Adapter/dp/B0002RNSKK?smid=ATVPDKIKX0DER

 

I've seen so many trailers that are wired incorrectly, even new ones. For some reason many trailers seem to be wired where the lights have to ground through the hitch instead of the ground being tied to the frame of the trailer, I always hook the ground directly to the trailer frame when I wire them.
That being said the OP needs to check the Towing Tail Fuse (30A) in the underhood fuse box and if that's good then check that the corresponding pins on the truck plug have power when they are supposed to.

 

Your first problem with one turn signal flashing both sides is a bad ground. To fix, clean the ground pins and sockets. While you're there, go ahead and clean all of the pins and sockets on the trailers and the truck. I suggest using rubbing alcohol and Q-tips. Then put silicone grease (bulb grease) on the ground pin to protect it from corrosion. While you're there, put it on all the pins. Then plug and unplug everything several times to spread the grease onto all of the pins and sockets. The grease will protect the metal from corroding and creating a bad connection.

Also put weather covers on the trailer plugs. If either or both sides of the 7-4 adapter are left exposed to the weather while unplugged, start storing it in the cab or put weather cover(s) on it, too.

What was said above about plugging and unplugging each plug several times when connecting a trailer is good advice.

Now about the running lights: Do the running lights on the truck itself work? If not, fix that. If so:

If cleaning the plugs and sockets didn't fix the trailer running lights, check the 30A Towing Tail fuse in the fuse box under the hood. If it's good, check the Towing Tail relay in the same fuse box. If I'm not mistaken, the inside of the fuse box cover shows the location of that relay. If not, put your finger on the Towing Tail fuse and move it in the direction of the Stop and OBD fuses. Keep going until your finger reaches the first relay. That relay is the Towing Tail relay.

 

some lights are self grounding, and if there is no connection (or poor connection) of your trailer chassis ground to trailer plug ground that’s the only way it’ll work.

A lot of times, with that long of wire travel and many connections, a ground reference gets a high resistance connection so that connection to the ball can provide that little extra reduction in resistance the trailer lights need to operate.

 

I have cleaned the pins and used dielectric grease. i have the plug with the test lights built in and the running lights on there wont come on. we tested the trailer lights on my dads with both the 7 pin adapter and with the reg 4 pin plug and eveything worked. yes the running lights on my truck work.

 

Time to start tracing back through the circuit to see where you lose power then. You have checked your fuses right?

 

I have had a similar experience - all circuits on the 4 way adaptor are good. Trailer lights were kind of intermittent, then after pulling the trailer out of my backyard, all lights worked, and worked the rest of the
season, no rhyme or reason - trailer lighting gremlin's. I know it is a ground issue, but short of rewiring the trailer, I just tow it a short distance and everything works.