Trailer turn signals won’t work if vehicle lights are on

Carolyn

We just replaced the taillights on our trailer (2009 T@da) because they were very dim and we noticed that the turn signal were almost not visible. The new LED trailights work great but we discovered that when the lights are on the brakes and taillights work but there is an almost non discernible  turn signal. When the lights are off all work as they should. Any thoughts?

tabiphile

If I follow this there was a weak turn signal before you made the lighting change. Now with new lights the problem remains...is that correct? I would start by checking the connections beginning with your 7 pin and working your way back. If you have a VOM you can (should) check voltages and look for either  corroded pins or a weak ground. The other obvious question is whether or not your new LED lights are drawing more voltage than the original one did? Often these replacements are not 100% pluga pluga.

falcon1970

I doubt the new LED lights are drawing MORE voltage than the old incandescent lights, but I do agree that the original problem was not in the lights but rather in the wiring.  I would start with the umbilical cord connection at the 7-pin.  Inspect both sides of the plug for corrosion and polish the pins and sockets--even a little bit of corrosion can cause a problem.  Use very fine (800 grit) good quality sandpaper.

Horigan

Could it be the quality or design of the LED lights?  What brand are they?  There should be two distinct levels of brightness to provide the taillight function and the brake/turn signal function.  Sounds like the lights are putting out two brightness levels that are very similar.  Have you confirmed voltage to both the tail light circuit (low intensity) and the brake/turn circuits (brighter) of the trailer wiring??

Carolyn

We tested the New LED lights before we sealed everything up and they worked beautifully but, it was the middle if the day and the truck lights were not on. Today when we were leaving the campground it was overcast so the auto lights were on and there was a very tiny blink if you looked very closely. With the lights off they work great.

rfuss928

I suspect a bad tail light ground. 

I have seen this happen.  The signal light gets ground through the running light filament when it is not lit and appears to function normal but can't ground when the running light voltage is present.

Try connecting a temporary additional ground wire to the wiring at the tail light to see if it resolves the issue.  If yes, then look for a problem with the trailer wiring.

Just an idea.  LED lights may act differently.

Good Luck.........

Bob

falcon1970

Where did you get the new LED lights?  Is it possible that they are not STT (Stop/Turn/Tailights but just Stop and Tailights?

Dalehelman

rfuss928 said:

I suspect a bad tail light ground. 

I have seen this happen.  The signal light gets ground through the running light filament when it is not lit and appears to function normal but can't ground when the running light voltage is present.

Try connecting a temporary additional ground wire to the wiring at the tail light to see if it resolves the issue.  If yes, then look for a problem with the trailer wiring.

Just an idea.  LED lights may act differently.

Good Luck.........

Bob

X2 sounds like a bad ground.

N7SHG_Ham

x3 on bad grounding.

BrianZ

x4 bad ground connection.
We had a similar issue on our utility trailer.  I followed the 4-pin cable back to the trailer's tongue, where I found the negative wire was screwed into the underside of the frame.  The screw was badly rusted & most of the strands in the wire were broken.  So, I cut it & stripped it back to good wire, soldered on a new loop connector, sanded all the rust from around the screw hole down to bare metal, then replaced the wire with a new screw and covered with dielectric grease.  It worked like new.

Carolyn

Here are some troubleshooting facts so far. When the truck is hooked up to the 2014 cs the turn signals function correctly but they are actually separate lights. When plugging a 7 pin tester into the truck the ground light flashes. This makes me think it might be the truck but why does it function properly on the cs and not the T@Da? The T@da functions perfectly if the truck lights are off. ????

rcuomo

X5 on bad ground. Very common issue with boat trailers. 

Cbusguy

If they were bought on Amazon it is very possible it is the lamp is incorrectly labeled at the manufacture.    This happened to me on my truck as someone earlier pointed out.      

BrianZ

@Carolyn, have you tried the 7-pin tester with truck lights on versus off, to see if the ground indicator is any different? (This may confirm your findings related to lights).  Also have you tried cleaning the 7-pin contacts on truck, tester & both trailers plugs, to see if that makes a difference? 

If you have a multimeter which measures resistance, it might be helpful to measure resistance between each plug & socket's ground contact and its respective trailer or vehicle's frame (using bare metal), to see if it indicates a good ground connection (a few Ohms or less) or a poor one (hundreds or thousands of Ohms).  Also check the tail lights' ground connection(s) between the light & trailer's negative busbar's connection.