LED backfeed question, how to prevent?

[TT_Vert]

Basically I have an RV that is now all LED lights and i notice the rear signal opposite side will faintly illuminate when I have my tow dolly plugged in. I thought perhaps it was a ground but i ran a new test ground and the problem persisted. Also goes away when I add more load by turning on running lights. Oddly this only happens in the rear. If i put in one incandescent bulb the problem goes away. My hitch adapter has LEDS which help to ensure wiring is functioning and it alternates L to R LEDS when either signal is on. I checked voltages at the trailer harness and I am seeing 12V to the element that should be lit and ~5V to the other side. Brake and turn use the same bulb LED panel. I took my decade resistance box to it and about 380 ohms it fixes it but i'd need at least a half a watt resistor on each side assume only a 30mA current which I'm sure it's more than that. I'd hate to have to wire in larger resistors to fix this.

Any input would be appreciated.

Dave

 

[dcg9381]

Interesting. The only time I've seen this is working on a microwave. I replace the incandescent bulb with an LED and it's lightly illuminated all the time.

Typically what you use to prevent backfeed is a "Rectifier diode". However, I'm not sure that this is what you want. As your LED is "lit" and LEDs are polar - this tells me that you're not getting backfeed, you're getting a potential difference somewhere.

Rigging LEDs to tail lights prior to the LED revolution, I'd often have to wire in a module that provided "typical resistance" so that the turn signal flasher would operate correctly. I think you've got some residual feed somewhere - it's not "backfeed"... And I think you're on the right path to burning that off by using a regular bulb or a small-enough resistor.

I wonder if the issue is your "hitch adapter" - I'd need to know more about that.

 

[TT_Vert]

Interesting. The only time I've seen this is working on a microwave. I replace the incandescent bulb with an LED and it's lightly illuminated all the time.

Typically what you use to prevent backfeed is a "Rectifier diode". However, I'm not sure that this is what you want. As your LED is "lit" and LEDs are polar - this tells me that you're not getting backfeed, you're getting a potential difference somewhere.

Rigging LEDs to tail lights prior to the LED revolution, I'd often have to wire in a module that provided "typical resistance" so that the turn signal flasher would operate correctly. I think you've got some residual feed somewhere - it's not "backfeed"... And I think you're on the right path to burning that off by using a regular bulb or a small-enough resistor.

I wonder if the issue is your "hitch adapter" - I'd need to know more about that.

It's not the adapter as It also did it when the trailer was not connected. Wired in a 380 ohm quarter watt resistor to both the ground and left and ground and right at the hitch itself and that fixed it. I left the signals on for quite a while and it never got above room temperature so I think I'm fine.

Dave

 

[ttpete]

Did you check the grounds for the lights? A bad ground is often the cause of that.

 

[andyvh1959]

Sounds like low voltage backfeeding the LED, which can cause it to light up, dimly. could need a diode on that circuit that keeps any voltage on the neutral side from backfeeding the light in question.

 

[dcg9381]

Sounds like low voltage backfeeding the LED, which can cause it to light up, dimly. could need a diode on that circuit that keeps any voltage on the neutral side from backfeeding the light in question.

It's the "backfeed" concept that I have trouble with. If the voltage is actually back-polarity (backfeed) LEDs will not function. It's got to be some residual voltage between ground and +12v.. If it's going the "right way" (right polarity) a diode won't help. And it shouldn't light if going the opposite way. <end IMHO theory>

A ground resistor is probably a good option to burn it off (like the OP did). LEDs are usually high impedance, so residual current goes through the lower-ohm resistor.

 

[rawen2]

This might not be much help but it really sounds like there is a bad ground somewhere. I had a similar problem on an older F150 that would dimly light up one turn signal indicator in the dash when the park or headlights were turned on. It would go out when the turn signal for that side was operating. After studying the wiring diagram I found that the left front park/turn bulb had corrosion between the base of the bulb and the socket.

 

[dave*99]

I worked on a fleet of new F-150s that have LED lights plugged into the trailer connector. The on board diagnostics complained that the trailer lights failed. I had to add load resistors to fool the the diagnostic system.
I suppose it expected incandescent trailer lights.

Old vehicles with exhibit a rapid blink on turn signals when incandescent bulbs are replaced with LED's. Again, load resistors are the cure. etrailer.com sells harnesses with resistors for this case.

Sounds like you found another case where they are the cure.

 

[TT_Vert]

I worked on a fleet of new F-150s that have LED lights plugged into the trailer connector. The on board diagnostics complained that the trailer lights failed. I had to add load resistors to fool the the diagnostic system.
I suppose it expected incandescent trailer lights.

Old vehicles with exhibit a rapid blink on turn signals when incandescent bulbs are replaced with LED's. Again, load resistors are the cure. etrailer.com sells harnesses with resistors for this case.

Sounds like you found another case where they are the cure.

My ground is good, actually ran a test ground right to the battery but I was pretty sure it wasn't a ground. I am using an LED flasher to fix the hyper flash. I have read about F150s having issues w/ this actually when I was doing research. They do make CANBUS compliant LEDs now for the problem you are describing.

Dave