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Not Getting Turn Signal Function When Using LED Bulbs On A Trailer  

Updated 07/16/2020 | Published 10/17/2010

Question:

Installed 1157 LED bulbs. If I hook up both wires to the tail lights I only have the brake light/flasher function, no tail lights. If I unhook the brake light/flasher wire the tail lights work. Do I need to install a resistor? Are the four incandescent maker lights causing the problem? Do I need to run a dedicated ground wire from the lights to the vehicle? Any info would be appreciated!!!

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Expert Reply:

LED bulbs have little resistance on their own, so when used with turn signals they can create a hyper flash situation, which is a fast flashing of the bulb. To determine if you will need a load-resistor kit like a LED Light Bulb Load-Resistor Kit # DI34ZR, you will install the bulbs and when the turn signals are activated, if the bulbs hyper flash you will need to install the load-resistor kit. This kit will prevent the turn signals from hyper flashing. You will need one kit for each LED bulb used in your turn signals.

I am sending a link that will show how to wire the load-resistor kit to your lights.

You will also want to make sure that the trailer lights are grounded. If the trailer lights have a white ground wire coming out of the light you will want to make sure that you have that wire grounded to a good clean metal area on your trailer. If the taillights do not have a white ground wire you will need to make sure the light is getting a good ground with the mounting studs. Some trailer lights are grounded by the studs that attach the lights to the trailer.

It is usually not a good idea to mix LEDs and incandescent lights, so if you have have side markers or other lights on the trailer, make sure you switch those to LEDs as well.

Incandescent lights draw much more amperage than LEDs do, and if they pull that current through the LED fixtures, the LEDs will burn up. We have LED side markers and clearance lights like part # MCL36RB, which is red or the # MCL36AB, which is amber.

expert reply by:
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Jeff D
Steven B. profile picture

Steven B.

7/11/2020

I replaced all of the incandecent lights on an EZ load trailer with LED lights including AL91RB AL91AB MCL66AB lights from etrailer. The lights all work correctly if I connect a 12 volt battery directly to each combination of the trailer light connector, i.e. right, left, brake, lights, running lights. If I connect my Toyota Highlander with a Uhaul trailer wiring connector to the trailer, only the tail lights work correctly, the turn signals do not work, and the side markers are very dim and flicker with the turn signals. When I test the Toyota's outputs, I get 12 volts output from all connectors and no apparent leakage. When I test the tow vehicle connector with the trailer connector (through a test wire connected to my voltmeter), I only get 8 volts output and the side markers do not light up or are very dim. Do know why the output from the Highlander drops from 12 volts to 8 volts when connected to the trailer? As I mentioned, both the trailer and Highlander seem to work correctly individually, but not when hooked together through the 4 way connectors. I cleaned both connectors and do not see any corrosion or obstruction. Can you tell me how to fix this problem? Thanks for your help with this problem.

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Chris R. profile picture
Etrailer Expert

Chris R.

7/16/2020

I'm thinking the voltage drop is a result of a weak ground somewhere on the trailer. Make extra sure that the white ground wires coming from each new LED assembly is securely attached to a CLEAN, bare piece of metal on the trailer. It might be worth it to even remove the grounds, sand down the surface, and reattach them. Let me know if this doesn't resolve the issue.
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