One weekend I have all trailer lights,  the next weekend,  I don't.   I have turn signals and brake lights,  no tail or running lights.   I bought one of those LED testers and was getting no indicator light on the tail light post.  I installed a new plug and still have nothing.  Any suggestions?

Sounds like a bad ground. It's sporadically grounding through the ball. Do you have a plug and play light add on or was it wired in?

 

What do you mean by plug and play or wired in?  Are you talking about the LED tester?

I think plug and play is when you can uncouple some wires and put the wiring harness inbetween and don't have to skin wire and use connectors. One thing you might try is to take your jumper cable and connect to the frame of the car and to the trailer. If it works then, you have a bad ground.

The truck has a harness that runs to the trailer plug,  no skinning.

You have blown the fuse for the trailer's running lights (tail and marker lights)..They are not on the same circuit as the tail lights on your tow vehicle.  Check your owner's manual under fuses.  it should have a schematic diagram with each fuse listed.  The trailer lights, brakes, signal etc., will trlr or something close that indicates the trailer circuits.  When you see trlr lts or maybe lights, that will be the fuse for your running lights.  Check that fuse before you drive yourself crazy.  Most trailers have a common ground for all the lights.  if you have brake lights, four ways, and turn signals that ground should be okay.

The below is for a 2014 Silverado.  The trailer lamps are fuses 14 - 17.  The parking/running lamps are #15.

Google (your year, make and model) fuse box diagram.  After the next page opens, click on "images" if you do not see some images to choose from. 

Good info

Dave I love the way you said "it worked yesterday".

Capt Mike

 

I was waiting for you...  

 

I knew you'd be along...

Check your connections at the rear,  if you have wire nuts pull them off and then put them back on to make sure the connection is tight

No nuts.  Straight from the harness to the plug.

Trailer lights only work in the driveway!

40 minutes ago, Catt said:

Trailer lights only work in the driveway!

But not on the parkway.

Did you get your problem resolved?  If so, what was it?  And how did you fix it.

One of my pet peeves is that someone asks for advice, and they get several suggestions, but we never hear about the resolution.

Please, if you ask for advice, let us know how things turn out.  it may help someone else.

It's common courtesy.

It was the fuse for the trailer tail lights.  Just had some time yesterday to dig into it. 

I put in a new fuse and the tester lit right up.  All but the left tail was on.

I pulled the cover off the light and found the plug was completely corroded.  When I tried to pull it apart,  one of the male pieces just crumbled and broke off inside the female side.

If thats what happened and you need a new light housing definitely go LED. I blew more bulbs when I ran regular lights. Walmart, $30, 2 hours and I had a new harness through my trailer with new lights which dont run the risk of blowing anymore!

Thank you for letting us know the outcome.  Glad it was just a fuse.