Who has LED headlights
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Veteran
Joined: Oct 2010
Posts: 290
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From: Columbia, TN
Who has LED headlights
I did some searching and didn't find hardly anything on led. Some info on hid which may be useful. Anyway i have a 2006 1500, i had a bulb go out and guys at work talked me into led. For some reason i pulled the trigger before researching. Anyways they work on high but don't work on low. If the truck is not running and key on the lows will work. Just curious if the people who have them had to run resistors or a canbus harness or run a relay setup.
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Joined: Dec 2017
Posts: 352
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From: Canada West
LED = Light Emitting Diode
A diode is an electrical one way device. Meaning current flows one way but cannot flow the other. For the mechanics guys, think of a diode as an electrical check valve. A diode also has a minimum voltage to over come before the flow starts. For the mechanics guys, a diode really is like spring loaded check valve.
If the LED lights are not turning on then one of two things is occurring. 1) The polarity of the source power is reversed, diode will not let flow through the wrong way (check valve). 2) Polarity is correct but the voltage is too low to get through (spring check valve).
bigreed91, for the problem with your lights as described I believe the polarity of the wiring on the lows is actually reversed. Swap the low beam wires in the headlight plug, not the truck plug, and they should work. This also explains why they do not work when truck is on but do work when truck is off. When the truck is on, the main voltage is high from the alternator which prevents any back current. When the truck is off, the alternator voltage is off and there is likely parasitic back current flow from somewhere that is finding a path through the low beam light diode. The back current being the correct direction through the reversed diode and so it lights up.
You can test this by unplugging the lights and use a separate battery and test wires to power up the light. Try connecting the test battery wires to the LED in different/reverse polarity and see which way lights them up. Then check the truck plug with a meter to see which polarity the truck is. Compare the two and correct the polarity of the connection to the light. No worries, no damage will be done while testing if you have the light disconnected from the truck and are testing the light only.
Reversed polarity on LED lights is a very common problem with aftermarket lights. Simply remove the wires from the LED side of the plug, swap them and reconnect the plug. Rewire the plug. Do not change the truck plug.
Hope that helps!
A diode is an electrical one way device. Meaning current flows one way but cannot flow the other. For the mechanics guys, think of a diode as an electrical check valve. A diode also has a minimum voltage to over come before the flow starts. For the mechanics guys, a diode really is like spring loaded check valve.
If the LED lights are not turning on then one of two things is occurring. 1) The polarity of the source power is reversed, diode will not let flow through the wrong way (check valve). 2) Polarity is correct but the voltage is too low to get through (spring check valve).
bigreed91, for the problem with your lights as described I believe the polarity of the wiring on the lows is actually reversed. Swap the low beam wires in the headlight plug, not the truck plug, and they should work. This also explains why they do not work when truck is on but do work when truck is off. When the truck is on, the main voltage is high from the alternator which prevents any back current. When the truck is off, the alternator voltage is off and there is likely parasitic back current flow from somewhere that is finding a path through the low beam light diode. The back current being the correct direction through the reversed diode and so it lights up.
You can test this by unplugging the lights and use a separate battery and test wires to power up the light. Try connecting the test battery wires to the LED in different/reverse polarity and see which way lights them up. Then check the truck plug with a meter to see which polarity the truck is. Compare the two and correct the polarity of the connection to the light. No worries, no damage will be done while testing if you have the light disconnected from the truck and are testing the light only.
Reversed polarity on LED lights is a very common problem with aftermarket lights. Simply remove the wires from the LED side of the plug, swap them and reconnect the plug. Rewire the plug. Do not change the truck plug.
Hope that helps!
Last edited by FaceDeAce; Feb 22, 2019 at 12:30 PM.
