Trailer Lights Not Working

[blang008]

I had to re-wire the 4 way flat plug on boat trailer. Running lights work, right turn signal works, right brake light works. When you let off the brake, both back running lights work, but when you press brakes only right brake light works. Any ideas??

 

[kenmyfam]

Re: Trailer Lights Not Working

I had to re-wire the 4 way flat plug on boat trailer. Running lights work, right turn signal works, right brake light works. When you let off the brake, both back running lights work, but when you press brakes only right brake light works. Any ideas??

3 biggest issues with trailer wiring are as follows.
1. Bad Ground.
2. Bad Ground.
3. Bad Ground.

Is the bulb OK ??? Has it ever worked properly ?? Was it OK before replacing the 4 flat ???
Welcome to iboats.

 

[blang008]

Re: Trailer Lights Not Working

3 biggest issues with trailer wiring are as follows.
1. Bad Ground.
2. Bad Ground.
3. Bad Ground.

Is the bulb OK ??? Has it ever worked properly ?? Was it OK before replacing the 4 flat ???
Welcome to iboats.

Yes sir, the lights have worked properly in the past. I checked the ground on the trailer side and it looked okay. They did not work before replacing 4 flat. Bulb looks okay. Thanks

 

[kenmyfam]

Re: Trailer Lights Not Working

Yes sir, the lights have worked properly in the past. I checked the ground on the trailer side and it looked okay. They did not work before replacing 4 flat. Bulb looks okay. Thanks

What was the reason for replacing the 4 flat ?? diagnosis or process of elimination ??

 

[Silly Seville]

Re: Trailer Lights Not Working

Back in the good 'ol days when the individual bulb sockets were grounded through the wiring harness with a "fifth" wire, it wasn't much of a problem. Now, with the plastic housings that use a cheesy bolt to carry the ground through the trailer frame...well that's where you get your bad grounding issues. I have gone so far as to solder an auxiliary ground wire to each lamp base and run those to a dedicated ground wire that runs back up the trailer to the tow vehicle wire harness connection, and tap directly into the white wire. That way, the light bulbs are grounded to the tow vehicle, instead of depending on the trailer frame.

 

[blang008]

Re: Trailer Lights Not Working

What was the reason for replacing the 4 flat ?? diagnosis or process of elimination ??

It had been smashed and no longer would attach to truck.

 

[ihaveabrownboat]

Re: Trailer Lights Not Working

Problem with ground to the left socket should affect the running light in that socket also. The left turn signal and left brake light are the same filament in that bulb and fed from the same wire to that bulb. Since those are the two functions not working trace that lead. Start with a test light on the contact in the bulb socket while the turn signal is on. If that contact is pulsing (blinking) you've got a ground problem. If not you're never getting brake light and turn signal power to it.

 

[kenmyfam]

Re: Trailer Lights Not Working

It had been smashed and no longer would attach to truck.

And before it got smashed it worked fine ????

 

[Grub54891]

Re: Trailer Lights Not Working

Back in the good 'ol days when the individual bulb sockets were grounded through the wiring harness with a "fifth" wire, it wasn't much of a problem. Now, with the plastic housings that use a cheesy bolt to carry the ground through the trailer frame...well that's where you get your bad grounding issues. I have gone so far as to solder an auxiliary ground wire to each lamp base and run those to a dedicated ground wire that runs back up the trailer to the tow vehicle wire harness connection, and tap directly into the white wire. That way, the light bulbs are grounded to the tow vehicle, instead of depending on the trailer frame.

I do that also,very seldom have any issues anymore

 

[UncleWillie]

Re: Trailer Lights Not Working

I had to re-wire the 4 way flat plug on boat trailer. Running lights work, right turn signal works, right brake light works. When you let off the brake, both back running lights work, but when you press brakes only right brake light works. Any ideas??

Running Lights Work = Brown Circuit OK.
Right Turn Signal Works = Green Circuit OK
Right Brake Light Works = Green Circuit OK
Only Right Brake Light works = Green Circuit OK; Yellow Circuit NOT OK!

Yellow = Left Brake/Turn Signals.

 

[kmarine]

Re: Trailer Lights Not Working

I think you have a bad ground. To test run a jumper cable from your car frame to your trailer frame and see if that solves the problemb It is the white wire on the 4 way connector. otherwise you will need to get a test lite and search for the short.