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Odd behavior with LED headlights

Number21

NAXJA Forum User
Location
NC
I recently put a set of LED sealed beam replacements in my '98 XJ. The light output is FANTASTIC compared to the candles I used to have, but I've noticed something odd. When my engine is running, and the headlights are turned off - they still light but much dimmer than usual. Almost like DRL, but my Jeep does not have that feature. I never noticed this with the old sealed beams.

Does anybody know how these are getting power when the headlight switch is completely turned off? Is there a short somewhere?

The reason it bothers me is because it always triggers the headlight delayed turn off, which I don't like. Usually I turn off the headlights before I shut off the engine, and they turn off immediately. If I shut off the engine and then the headlights, they stay on for about a minute. This feature is being triggered regardless of whether I turn off the engine or the headlights first, because of the power leakage.
 
Why is there any voltage here at all? Where is it coming from? If the headlight switch is off...that's it...it should be a dead circuit. I don't have DRL or fog lights.
 
Neither one of you guys mention what headlights you're using -- not going to matter with the stray voltage issue, I'm just wondering what brand you're using and if they are any good

If I mention a brand this thread will just turn into off topic brand bashing and arguing about which headlights are better. I will PM you the brand, I would prefer this topic stay on topic please.
 
Mine do the same. A portion of my LED's light when running. Another portion comes on with low beam switch...another with hi beam switch. Turn off engine b4 light switch & they stay on a minute.
I think the circuitry is designed that way. Never have drained the battery, I believe there is no stray voltage, with engine on or off.

I haven't looked at schematics, but it is possible to feed voltage to the lights thru 2 different paths. Therefore, I beleive even though your light switch is off...they may have designed the lights to have voltage fed to lights when engine is running.

Hope I made sense...hee hee.

Love my LED's...even though sometimes out on my acreage I would like complete darkness out of my lights.
 
Normal incandescent bulbs won't light with low voltage. All brands of LED's are very efficient and often will light with even the tiniest amount of voltage.

Install some 12 volt Diodes on all wires to the headlamps. Diodes are a one way electrical valve that will prevent stray voltage from backfeeding.
 
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Does anybody know how these are getting power when the headlight switch is completely turned off? Is there a short somewhere?
When the headlight switch is off and the headlight delay timed out, there should be no power at the headlight.
The delay feature should not happen if the headlights are turned off before shutting the engine down. Something is not right.

Power is delivered to the headlight though the low-high beam switch or the headlight delay module.
If power still still flowing, when the headlight switch if off, either the headlight switch is going bad or there is a problem with the headlight delay module circuit.
Unplug the delay module and see if the problem persist.

This would be a good time to get the multimeter out and start tracing the power from the headlights back toward the battery, to determine where the phantom voltage is coming from.
A FSM's schematic of the headlight wiring will make the troubleshooting a lot easier.
 
When I was trouble shooting the front end lights on my Jeep after installing LEDs I found numerous issues with the wiring harness for the lights: shorts, corrosion causing arcing, bad plugs etc... I ended up rewiring the whole circuit and adding diodes to correct the lighting behavior. There are numerous places where phantom voltage can be back fed to the light circuit and LEDs don't offer enough resistance to stop it and will light at very low voltages. Most LEDs used in automotive applications are stable from 4 volts to 36 or even 48 volts.
 
Can anybody tell me where the headlight delay module is located in my '98? Would be easy to pull out and see if that is the problem - but also might just leave it out either way, I really don't like that feature.

This isn't really that big of deal, mainly I was just very curious where the power is coming from. And the delay is annoying. It actually makes them function like DRL, which isn't bad really.

I appreciate the information.
 
It's under the dash on the drivers side.

You sure about that? I don't see anything on the driver side that looks like it would be the delay module. I pulled the #9 fuse on the passenger side, which is for the headlight delay and cluster, and it did indeed stop the headlights from lighting when they shouldn't. But, it also kills the cluster so I can't leave that out.

Is the delay one of the three relays in the fuse box on the passenger side?
 
Pro demand says the headlight delay module is behind the left side of dash

There are 2 red/white wires coming from the headlamp switch -- One goes to the PDC in the engine compartment the other goes to the Headlamp delay -- Maybe it's possible to follow the wire
 
Flashlight spam aside, its interesting to see this thread filter to the top, because my LED head lights are doing the same thing. Rather fascinating that there is any voltage with the lights off. I think its a nifty feature, even if it does mean there is an issue with the headlight circuit, although I'm not convinced that there really is an issue with the circuit. Based on the LEDs that it lights up, the low voltage appears to reside in the low beam circuit. At some point, I may remove a headlight to see what the voltage actually is.
 
I have the same issue with my 89. The issue goes away if i leave the headlights on high beam when the switch is off.
 
I recently installed a set of Angel Eyes LED headlights which
include the DLR feature, and they do not illuminate with the
switch off. It's a 96 model.

Since this issue occurs with the low beams only, I suspect there's
voltage leaking through the multi-function switch somehow, to the
low beam circuit.

If this is true, the cure would be to install a new multi-function switch.
 
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