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post #1 of 16 Old 04-17-2009, 06:00 PM Thread Starter
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voltage to headlights

I finally got around to wiring my driving lights. I used the hot wire from the high beams to power the switch so that they only work when the high beams are on. While figuring out which wire was the high beam wire with my multimeter, I was surprised to find that when either the high beams or low beams are not on, they still have 4 volts of power going to them. Why is that?

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post #2 of 16 Old 04-18-2009, 02:07 PM
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Maybe it has something to do with the can bus system. ???

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post #3 of 16 Old 04-18-2009, 02:14 PM
 
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I wish I knew....So is the headlight system one you can replace with halogen bulbs or do you have to replace the whole head lamp? I have not checked yet stupid question I know. I have asked at 2 separate wheeling shops neither knew the answer.
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post #4 of 16 Old 04-18-2009, 04:14 PM Thread Starter
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Yep. The bulbs just twist out of the back of the reflector. Very easy.
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post #5 of 16 Old 04-18-2009, 06:35 PM
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If you want more light, the bulbs are only part of the problem.
The reflector unit itself is crap.
If you want more light, swap in a set of Delta headlights for $100, not much more dinero than a pair of good bulbs but big difference.
If its still not enough, rewire with heavy gauge wire to the battery and use the factory wires to trip relays.
Plus the Deltas use H4 bulbs, much larger selection of replacement bulbs.


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post #6 of 16 Old 04-19-2009, 04:52 AM Thread Starter
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Do the deltas have glass lenses?
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post #7 of 16 Old 04-19-2009, 06:14 PM
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Quote:
Originally Posted by woodys3b View Post
I finally got around to wiring my driving lights. I used the hot wire from the high beams to power the switch so that they only work when the high beams are on. While figuring out which wire was the high beam wire with my multimeter, I was surprised to find that when either the high beams or low beams are not on, they still have 4 volts of power going to them. Why is that?

Thanks
Andy
These headlights are not driven off a relay. They are driven off a solid state switch in the Totally Integrated Power Module. These switches can be designed to 'leak' any amount of current through their respective loads even then the device is supposedly turned off. The engineers have chosen to run this small current through the lights to check if the bulb is burned out or shorted to ground. The current is not large enough to light the lamp, but can reliably indicate a bad bulb. If your headlamp burns out, the computer will set a code and your Malfunction Indicator Lamp will come on because the computer's not happy. Fix the problem and your Jeep will be happy again.

That's why you see a voltage when the lights are turned off.

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post #8 of 16 Old 04-20-2009, 04:23 PM Thread Starter
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Thanks Alter Ego. That makes perfect sense.

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post #9 of 16 Old 04-20-2009, 05:47 PM
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Do the deltas have glass lenses?
yup


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post #10 of 16 Old 04-21-2009, 10:14 AM
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Quote:
Originally Posted by Alter Ego View Post
These headlights are not driven off a relay. They are driven off a solid state switch in the Totally Integrated Power Module. These switches can be designed to 'leak' any amount of current through their respective loads even then the device is supposedly turned off. The engineers have chosen to run this small current through the lights to check if the bulb is burned out or shorted to ground. The current is not large enough to light the lamp, but can reliably indicate a bad bulb. If your headlamp burns out, the computer will set a code and your Malfunction Indicator Lamp will come on because the computer's not happy. Fix the problem and your Jeep will be happy again.

That's why you see a voltage when the lights are turned off.
Is that enough to trip a relay if I choose to rewire with heavier gauge wires and use the stock wires to control new relays?

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post #11 of 16 Old 04-21-2009, 11:29 AM
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Is that enough to trip a relay if I choose to rewire with heavier gauge wires and use the stock wires to control new relays?
That 4 volt measurement was probably taken without the bulb in the circuit so the multimeter would have been the only load. Once you load the circuit with a wirewound relay coil, I bet that voltage drops way down.

I've read several posts of people hooking up relays to headlights and factory fogs to run bigger lights on their JK. None of them reported any problem with that setup, so I'll guess that it should work allright. I've never tested it personally so it's just a guess for me.

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post #12 of 16 Old 04-21-2009, 12:17 PM
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Quote:
Originally Posted by Alter Ego View Post
I've read several posts of people hooking up relays to headlights and factory fogs to run bigger lights on their JK. None of them reported any problem with that setup, so I'll guess that it should work allright. I've never tested it personally so it's just a guess for me.
There are some problems hooking up a relay to the headlight circuit but it is easily fixed. The voltage to the headlights is pulse width modulated and will cause the relay to "chatter". It is corrected with a simple capacitor across the coil leads.

I would search out the posts where they corrected this issue and follow what they did.

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post #13 of 16 Old 04-21-2009, 04:25 PM Thread Starter
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Wow, this is getting complicated. I used the hot wire for the high beams to power the relay via a lighted switch on the dash. Even though I saw 4 volts (bulb removed) when low beams were selected, the relay seems to work fine. How can I tell if the relay is chattering? I didn't hear anything.
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post #14 of 16 Old 04-21-2009, 05:02 PM
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Here is a link to the thread about it over on Jeep Forum:

http://www.jeepforum.com/forum/showthread.php?t=668241

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post #15 of 16 Old 04-21-2009, 07:07 PM
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OK, the cap I understand, to integrate the PWM waveform. But what's the diode for? To protect the driver transistor from field collapse? I've always seen these in parallel with the coil, not in series. New relays have them built right in. I thought that was sufficient. What am I missing here?

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post #16 of 16 Old 04-21-2009, 08:22 PM
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I do not know why he has the diode in series, it's not my circuit. Like you said I have one in parallel on the coil for my winch disconnect solenoid to protect the LED indicator from the field collapse. I learned this from frying more than one LED.

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