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Led head lamp swap

John ablessed

New Member
So i have a 2011 nissan frontier (i will put a picture of what schematics i pulled off the dealer below) and i decided to add a few mods being an electrician myself. First i added a 26 inch led light bar i put the light bar on a three position switch that gives constant power to the light bars relay if i want it to and in the other position it allows my light bars relay to be triggered by my high beam leaver. So when i turn on high beams my light bar comes on as well (if switch is in said position). So because i live in canada my truck has day time running lights that work by giving reverse polarity to the high/low beam light. So naturally when i spiced into the high beam wire To feed my relay i had to put a diode (1N4004) in series’s with my light bar relays coil. I later decided to swap my old head Light bulbs for led Bulbs. When i did this i noticed only one headlight will light up as day time running lights but they both work high/low. I believe this is because my headlights are In series with eachother and only the one i spliced into (to feed relays coil) is the one that is turning on. My theory is because the leds head light bulbs draw less power There is to little resistance for my diode. So i have some questions. One time i opended the door and all the interior light were flickering as if my bcm was shorting do you think i have done damage to my bcm and secondly how do i fix this problem what type of diode would i need? Do you think i did any damage? I havnt noticed anything wrong yet
 

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rjenkinsgb

Well-Known Member
Most Helpful Member
One headlamp is connected with reverse polarity while in running light mode.

LEDs are polarity sensitive so unless the lamps are specifically designed to work either polarity [which would involve rectifiers and power loss], the reversed one will not illuminate.
 

Diver300

Well-Known Member
Most Helpful Member
The daytime running function on main beam puts both headlights in series, therefore running them on about 7 V each, with one reversed. That relies on the headlight bulbs:-
1) being about quarter brightness on 7 V
2) sharing the voltage equally
3) working the same with reversed polarity

White LEDs are 3 V each, and so LED bulbs are made of several LEDs and some driver circuit. Without knowing a lot more about the driver circuit, the LED bulbs could fail any or all of the three conditions. I've never seen a circuit that would meet all of those three conditions. It would be possible to design one that did, but it would cost more and the LED bulb manufacturer would have little reason so do that. Your LED bulbs may not be suitable for dimming at all.
 

John ablessed

New Member
The daytime running function on main beam puts both headlights in series, therefore running them on about 7 V each, with one reversed. That relies on the headlight bulbs:-
1) being about quarter brightness on 7 V
2) sharing the voltage equally
3) working the same with reversed polarity

White LEDs are 3 V each, and so LED bulbs are made of several LEDs and some driver circuit. Without knowing a lot more about the driver circuit, the LED bulbs could fail any or all of the three conditions. I've never seen a circuit that would meet all of those three conditions. It would be possible to design one that did, but it would cost more and the LED bulb manufacturer would have little reason so do that. Your LED bulbs may not be suitable for dimming at all.
Yeah but the weird thing is, when disconnect the wire i used to tap into the highbeam wire coming from my headlight assy, the day times dont turn on. When i connect that wire back (which goes to my light bars relay) which is probaly giving it a ground path through my relays coil, the led headlight bulb lights up as a day time running light. I believe my led light bulbs are drl capable. It would make sense how when i connect it to my relays coil the left headlight turns on as a day time but both work normally.
 

Diver300

Well-Known Member
Most Helpful Member
Yeah but the weird thing is, when disconnect the wire i used to tap into the highbeam wire coming from my headlight assy, the day times dont turn on. When i connect that wire back (which goes to my light bars relay) which is probaly giving it a ground path through my relays coil, the led headlight bulb lights up as a day time running light. I believe my led light bulbs are drl capable. It would make sense how when i connect it to my relays coil the left headlight turns on as a day time but both work normally.
I can't follow what is going on without a circuit diagram.

The "DRL capable" LED lamps may dim on a lower voltage, so that might be that they meet my condition 1), but I'm not sure.
 

John ablessed

New Member
I can't follow what is going on without a circuit diagram.

The "DRL capable" LED lamps may dim on a lower voltage, so that might be that they meet my condition 1), but I'm not sure.
Its a bit much but heres my trucks schematics. Im thinking since the leds have less resistance the current spiked and my diode isnt enough to stop the left led headlight drl from taking the path of least resistance through my light bars relays coil. (Not shown on diagram)
CF24A9E7-0AFA-4C54-8B5B-61841EC126A8.png
 

Diver300

Well-Known Member
Most Helpful Member
Yeah but the weird thing is, when disconnect the wire i used to tap into the highbeam wire coming from my headlight assy, the day times dont turn on. When i connect that wire back (which goes to my light bars relay) which is probaly giving it a ground path through my relays coil, the led headlight bulb lights up as a day time running light. I believe my led light bulbs are drl capable. It would make sense how when i connect it to my relays coil the left headlight turns on as a day time but both work normally.
I think that the relay coil is providing a ground path for the left headlight. That would imply that the lights work with reversed polarity.

However, I can't see any solution to getting the LED lamps to work at reduced brightness when in series.

Also, with incandescent lamps, I think that your light bar relay will be running on 7 V or so with the DRLs on, which might be enough to make it turn on.
 
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John ablessed

New Member
I think that the relay coil is providing a ground path for the left headlight. That would imply that the lights work with reversed polarity.

However, I can't see any solution to getting the LED lamps to work at reduced brightness when in series.
Thats fine, i dont mind if the drls dont work i just dont want the left one lit up while the right one is off, it makes it look like a headlamps out. So since the relays coil is giving a path to ground shouldnt a diode in series with the relays coil to the fix? I have a 1n4004 right now it seems i need a bigger diode no?
 

Diver300

Well-Known Member
Most Helpful Member
I don't think that a different diode would work.

If you disconnect one of pins 1, 2 or 5 of daytime running relay 1, that will stop the DRLs working. You will have to leave pins 3 and 4 connected or the left headlight won't work.
 

John ablessed

New Member
I don't think that a different diode would work.

If you disconnect one of pins 1, 2 or 5 of daytime running relay 1, that will stop the DRLs working. You will have to leave pins 3 and 4 connected or the left headlight won't work.
Interesting. If i flip the switch which disconnects the high beam wire from the relays coil, the left drl light goes off So it seems like cutting its continuity to ground will do the fix. Why would i diode not be the solution if i may ask? Wouldnt the diode be cutting its path to ground
 

Diver300

Well-Known Member
Most Helpful Member
Taking the wires off the relay won't cut the continuity to ground. It will do the opposite. It will leave the common connection for the left headlight connected permanently to ground.

In the unmodified state, the common connection for the left headlight is connected to the battery to make the main beams turn on as DRLs. The current flows backwards through the left main beam filament, then through fuses 34 and 35 and through the right main beam filament to

Disconnecting one the of the wires I suggested will stop that happening.
 

John ablessed

New Member
Taking the wires off the relay won't cut the continuity to ground. It will do the opposite. It will leave the common connection for the left headlight connected permanently to ground.

In the unmodified state, the common connection for the left headlight is connected to the battery to make the main beams turn on as DRLs. The current flows backwards through the left main beam filament, then through fuses 34 and 35 and through the right main beam filament to

Disconnecting one the of the wires I suggested will stop that happening.
Cant i just pull the fuse? Would that work?
 

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