Head lights won't come on but running lights do. - JeepForum.com
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  • 2 Post By shok47
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post #1 of 9 Old 09-09-2019, 08:09 PM Thread Starter
Joncure
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Head lights won't come on but running lights do.

So when I pull the light switch out to first position, the running lights come on like they should. I pull the switch out all the way and the head lights won't come on. What's the problem here? Bad ground somewhere? Maybe the switch is going bad? What else could it be?

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post #2 of 9 Old 09-09-2019, 08:36 PM
BagusJeep
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Sounds like you need to get a wiring diagram and, once you understand the simplicity, go through with a test lamp finding voltage.

The headlights are not fused, they are fed from the light switch via momentary circuit breaker inside the switch. Sometimes this fails, it is mechanical. I would start off by looking for voltage here from the red wire and out of the switch on the correct output tab along alight grey wire. Depends on which year and which switch you have (see below).

Power then goes down a light grey wire to the foot dimmer switch. The switch will send it out on one of two terminals (you can tell which is which, the hi beam terminal has two wires, one goes up to the hi beam light on teh dash) (LO is light grey, Hi is light grey with tracer). These switches break, they are abused, wet and dirty and the wires get knocked off the back. Check here for voltage.

Power then carries on out to the headlights, if stock. Many have put in relays near the headlights, you should check your wires actually go straight to the lamps.

If the lamps work, the other side is grounded to the grille. A daft place to ground them. A bad earth here or through teh body / frame / block back to the battery will stop them from working.

Perhaps this will help. You can see the "instrument panel lamp switch" on the right but it leaves out the downstream feeds to the lights, included the diagram so you can see the headlights are not fused. (light switch pic stolen from John Strenk, thanks John )
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post #3 of 9 Old 09-09-2019, 08:40 PM
shok47
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Hi,

I would check the hi/lo beam connector. Put a wire brush to the tabs and shine em up.

I had similar issue, were if I wiggled the connection, hi/low all work, not at all or 1 only.
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post #4 of 9 Old 09-09-2019, 08:51 PM Thread Starter
Joncure
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Thanks guys!
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post #5 of 9 Old 09-10-2019, 04:58 AM
Axhammer
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I would have cycled the hibeam switch several times on the spot before doing anything else. Old cars with old switches like to be cycled on occasion, it cleans the corrosion off the contacts
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post #6 of 9 Old 09-10-2019, 05:47 AM
jeepdaddy2000
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The next step on Bagus's post is to purchase a test light and troubleshoot the issue.
Turn on the light switch and check for power at the high/low beam switch.


If you have power going in but none going out, then the switch is bad.


If you have power going in and out, then the issue is between the switch and the lights. Check for power at the junction on the fender, then at the rear of the lights themselves. If you have power at the lights, then check the grill/bucket ground.


If there is no power at the high/low switch, then the issue is between there and the switch (we know the switch has power since the marker lights work). Drop the switch and check for power (use Bagus's diagram). If you have power in but none going out, then the switch is bad.

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post #7 of 9 Old 09-10-2019, 06:40 AM Thread Starter
Joncure
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Thanks jeepdaddy, that breaks it down simple enough for my skills! I did cycle the hi/lo switch several times with no effect. Test light procedure is next up.
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post #8 of 9 Old 09-10-2019, 10:29 AM
John Strenk
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Here is a little closer picture of the dimmer switch

C100 is the bulkhead connector on the firewall.
C105 is the plug that goes into the dimmer switch

You may or may not have the factory fog light switch so that plug will be left hanging if no fog lights
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post #9 of 9 Old 09-11-2019, 08:38 PM Thread Starter
Joncure
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Thanks everyone. Just as I was about to start using the tester light, I jiggled the wires coming out from the back of the switch on the dash and the head lights would come on and off with the jiggling. I'm guessing that either the switch is going bad or the connections are loose or corroded inside the switch. As I jiggled the wires the parking/running lights were not affected.
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