Hello everybody...kind of a newbie question here...

I just bought a 16ft utility trailer and it has the 4 pin wire harness. All of the running lights work but I have no brake lights and no turn signals. I know the main brake lights are dual function and the filaments in both main light bulbs look good. The wire harness also has this purple jelly like stuff on it that has now also gotten on the truck side from noeing connected and disconnected several time over the past week. Do you think this jelly stuff on the harness could be the cause of my no brake light and no turn signal issues?

 

Could be dielectric grease on the connection, did you try with new bulbs in the lights and make sure you are getting power to your 4pin on the truck

 

check that you have a ground.. at tow vehicle and on the Trailer. broken wire, Rust....


Do not rely on the Ball providing a ground...

 

At the risk of insulting . . .

Is the truck side good? If this was not checked, either a multi-meter or test plug (or another known good trailer) will isolate the truck.

 

This is GOOD input! I chased non-working brakes on the trailer for an hour before I did this...the issue was on the truck side.

 

It sounds like you might have a bad ground connection. When the taillights are on, that is when there is the most power draw on the system. Stepping on the brakes would then add more and this is when a ground problem will usually show up. https://www.carid.com/trailer-lights/ require constant maintenance - check for a bad ground, loose connection, and dirt and corrosion. Any of those can cause this problem.

 

Jay nailed the first step for you to take in troubleshooting.

Though grounds potentially COULD be your problem, since your running lights are working, though certainly not impossible, it's LESS likely that is where your trouble lies. The usual symptom for a bad ground is that the running lights will dim in rhythm with the flashers.

The signals you are lacking are usually output through 7-1/2-amp fuses in the truck, and those may need to be installed if this is your first trailer hookup.

If you need a wiring diagram for your specific truck, let us know the model and year. We may be able to come up with one for you.

The grease should be of absolutely no concern.

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