After replacing truck lights with LED's, TT lights act weird

[Bear25314]

I have a 2011 F250. I replaced all the marker light bulbs with LED's. Now, when I attach my TT, the marker lights on the TT act differently. The brake lights work fine, however, when I turn on a blinker (either one), all the marker lights begin to blink as well. Also, when I press the brake with the blinker on all the marker lights on the TT come on steady. I am at a loss. Thanks in advance for any pointers.

[Bear25314]

Thanks for all help Everyone. I tried a few different things but could not fix the problem of the trailer lights all blinking (marker lights and all) whenever I used the truck blinkers while hooked up to the TT. I ended up removing the led bulbs I put on the truck 1 by 1. I started with the front truck marker lights and worked my way to the back brake truck lights. When I removed the truck brake light leds and replaced them with the original incandescent brake lights the trailer lights now acted normal. I don't really get it but I guess I'll just leave it like that. Thanks again and I hope this helps someone else.

[Bear25314]

Thanks for all the replys Everyone. I tried to find a short or a ground problem but nothing I did changed anything. I ended up removing the led bulbs from my truck (brake lights) and that did the trick. I can live without those. Thanks again!

[westend]

I'd suggest that before you start removing marker light fixtures looking for a bad ground, try a couple of easy measurements at the truck's umbilical socket.

With the truck's lights on and a turn signal indicator operating, measure voltage at the different pins of the truck's connector, including the ground pin. I think what you'll find is that there is power on pins that should not be powered, notably, the truck's ground pin connector. This is how the incandescent marker bulbs on the trailer are being powered.

I sometimes forget that LED lights are not "bulbs" as in reference to incandescent bulbs. They are a diode, a device that lets electricity pass in one direction and not the other. The light that comes out of the diode is a byproduct of that current flow.

[Bear25314]

Yes, the trailer lights are blinking. The truck lights work fine. Thanks so much. Ill start looking at the trailer light ground then.

[beemerphile1]

Bear25314 wrote:

Would the bad ground be in the truck or the trailer?

It is the trailer lights that are blinking, right? You have a bad ground at the trailer tail lights and it is seeking a ground through the marker lights.

[Bear25314]

llr wrote:
It sounds like a bad ground at one of the tail/brake/turn combination lights. A bad ground here will will put power on the taillight circuit when the brake/turn is on or brake/turn when the taillight is on

Would the bad ground be in the truck or the trailer?

[llr]

It sounds like a bad ground at one of the tail/brake/turn combination lights. A bad ground here will will put power on the taillight circuit when the brake/turn is on or brake/turn when the taillight is on

[wa8yxm]

DownTheAvenue wrote:
Unlike incandescents. LED's have a specific positive and negative.

Many LED lights are designed with a bridge rectifier on the power line so they could care less which lead is positive, they figure it out, I have several where if I reverse the leads, work perfectly.

[beemerphile1]

Gdetrailer wrote:

beemerphile1 wrote:
I think the LED change is only coincidence, you have a bad ground in the trailer.

Try again.

OP HAS a 2011 F150 Ford Truck..

Ford for MANY years (at least back to 1997 uses RELAYS for the trailer lights.

NOTHING on that trailer wiring should affect how the truck lights work or operate....

The OP said;

Bear25314 wrote:
...when I attach my TT, the marker lights on the TT act differently.....

[tempforce]

some marker lights blink with the turn signals. if yours are designed to do that. the lights are not receiving enough grounding through the marker lights. when the turn signals are turned on.
also you may have a trailer ground issue as mentioned above.

[Gdetrailer]

beemerphile1 wrote:
I think the LED change is only coincidence, you have a bad ground in the trailer.

Try again.

OP HAS a 2011 F150 Ford Truck..

Ford for MANY years (at least back to 1997 uses RELAYS for the trailer lights..

NOTHING on that trailer wiring should affect how the truck lights work or operate.

I think it is coincidental at best when trailer is connected that the truck lights misbehave.

The problem IS the aftermarket LED lights on truck.

Put the original incadescent lights back in and problem should go away.. PROVIDED the LEDS did not DAMAGE the BCM (Body Control Module)..

All of the lights on the truck are directly connected to the BCM and the BCM is easily damaged..

If the BCM finds a fault in any of the outputs it WILL temporarily disable the output.

If the fault continues to exist the BCM CAN PERMANENTLY DISABLE THAT OUTPUT.. When that happens REPLACEMENT of the BCM may be the only way to restore the function.

But as I mentioned before, ALL of the lights on the trailer side ARE connected via RELAYS so the trailer lights are not directly connected to the BCM.. This prevents the trailer from damaging the BCM by accidental overload or shorts.

Not a good idea to mess with modern day vehicle electrical systems.

[Harvey51]

I'm sure blinkers have been modernized. The replacement I bought at NAPA several years ago had a chip in it and no bimetallic strip.

Monitoring the voltage across one of the lights might be informative. It would be interesting to check the voltage from each side of a misbehaving bulb to ground. "It happens when I attach the TT" certainly suggests something in the TT is feeding a small current back from one lighting circuit to another. Yes, I think a grounding problem could be the culprit. I would find a good ground on the truck and use a wire to connect to a good ground on the trailer for starters. Or even use the ground wire to ground one of the misbehaving lights to see if it has any effect.

Think of it as an interesting puzzle to avoid impatience and maybe you can enjoy figuring it out. Please let us know how you solve it!

[beemerphile1]

I think the LED change is only coincidence, you have a bad ground in the trailer.

[Bear25314]

Yes. This only happens when I have the trailer connected to the truck. The lights on the truck when disconnected work perfectly.