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Short Curcuit Causing Interior Lights To Not Work.


 
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Maxximmillian
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Joined: 28 Nov 2006
Location: Minnesota - Twin Cities

PostPosted: Tue Dec 26, 2006 2:29 pm    Post subject: Short Curcuit Causing Interior Lights To Not Work. Reply with quote

What would be causing all of the interior lights to short out? After replacing the fuse all the lights have power but only one works, and shortly after the new fuse blows. It calls for a 10 amp fuse, would putting a larger fuse in help the problem?
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dancerman
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Joined: 08 Jun 2006
Location: Atlanta

PostPosted: Wed Dec 27, 2006 3:13 am    Post subject: Reply with quote

You said it. You have a short circuit. If you put in a larger fuse, you risk a fire. The short could be a wire or a switch or a light socket. You will need to trace out the problem circuit so you can test each component individually starting at the fuse and working through to the switch and then each light socket.
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Maxximmillian
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Joined: 28 Nov 2006
Location: Minnesota - Twin Cities

PostPosted: Wed Dec 27, 2006 11:54 am    Post subject: Reply with quote

I'm extremely inexperienced with electical work. How will I know where the short is? What would be the "signs"? I'm inexperienced, but not dumb, so with a little bit o' help I should be able to figure it out. Thanks again, folks.
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dancerman
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Joined: 08 Jun 2006
Location: Atlanta

PostPosted: Wed Dec 27, 2006 2:32 pm    Post subject: Reply with quote

A few questions.

What year is your XJ?

Which interior lights are not working?

Have you checked all the bulbs? Which one still works? How do you know they have power if some are not working?

Does the fuse blow if you do not turn on the lights or only after you switch them?

If the fuse blows without switching the lights them the circuit is shorted between the fuse and switch (and it could be the switch). If it's only after you switch them, then the short is after the switch (it could be the switch in this case, too).

I have a manual with some wiring diagrams so I can look it up for you.
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Maxximmillian
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Joined: 28 Nov 2006
Location: Minnesota - Twin Cities

PostPosted: Wed Dec 27, 2006 3:32 pm    Post subject: Reply with quote

ok, the answers to your questions:

My Jeep is an '89 XJ two-door.

The interior lights that aren't working:
-under-dash lights on driver and passenger side.
-dome light
-rear dome (cargo) light

I have checked all of the bulbs and they are all good.

The bulb that works with a replaced fuse is the spotlight over the passenger seat. I'm not sure if the driver-side spotlight works because I couldn't figure out how to get to it to check if it was burnt out.

I know that the lights are getting power because I tested them with a circuit tester. When testing them, the tester lit up when I touched it to both contacts. There didn't seem to be a positive and a negative, because like I said the tester lit up when I touched both. Could this be an indication of the problem?

I replaced the fuse and then the spotlight over the passenger seat began to work, but a short while after that as I was checking the other lights for power, the light shut off, none of the other lights had power anymore, and I found that the fuse had blown.

*Now I have another question: My instrument cluster lights do not dim when the knob is turned. I also do not feel the knob "click" as if I were turning on the interior lights. Do you know what I'm talking about? Do Jeeps work the same way as most other cars with that style of headlight/interior light switch? If they do, could the failure or malfunctioning of that switch possibly be causing my problem?

I know this is a lot of information and some unorganized questions, but you've been a lot of help already and I really appreciate your insight and expertise. Thanks again to anyone who can help.
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dancerman
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Joined: 08 Jun 2006
Location: Atlanta

PostPosted: Thu Dec 28, 2006 4:26 am    Post subject: Reply with quote

Your answers help.

The map lights (spots), although on the same fuse, use a separate switch. So it makes sense that they could be working when the others are not (until the fuse blows). I suspect the driver side bulb is out. I would turn them off for now.

I want to be clear on what you are saying.. that each bulb contact has voltage. Meaning, you attached one lead of your tester to the chassis and tested each contact separately and found power at both. If so, that's a problem. One contact should be power and the other be grounded when the circuit is switched on (door open). The only way power to both contacts is possible is if (1) one of the bulb sockets has a short (allowing both contacts to be connected) or (2) the headlamp switch is somehow feeding power into the ground side. You should carefully inspect each bulb socket to make sure they are good. You may have to remove each one and use an ohm-meter to insure each contact is electrically independent. Look for frayed wires or corrosion.

And yes... your headlamp switch should dim the dash lighting when rotated and click to switch on the interior lights. If it doesn't, then this may be your problem. You could disconnect the connector from the headlamp switch and see if the interior circuit works normally and does not blow the fuse. If it works then it's likely the headlamp switch causing the problem.
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Maxximmillian
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Joined: 28 Nov 2006
Location: Minnesota - Twin Cities

PostPosted: Thu Dec 28, 2006 9:44 am    Post subject: Reply with quote

Oh man... you've been such a help. I've not tried anything yet, but I jsut wanted to let you know that your help is definitely appreciated. I will have to try disconnecting the headlight switch first. But what you described with both of the contacts getting power is truly what's happening. I'm thinking that that problem may be a little more difficult than just a bad switch in the dashboard. However, knowing nothing about wiring and switches, I may very well be wrong. Thanks again and I'll give you an update in a day or so.
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kaos
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Joined: 10 Jan 2006
Location: Iceland

PostPosted: Thu Dec 28, 2006 1:00 pm    Post subject: Reply with quote

Note that power on both contacts is normal if all of the following conditions are true:
1. There is a bulb in another socket on the same circuit (the cargo light, footwell lights, etc.).
2. The negative side is "floating" (i.e. the lights are off).
3. Your tester is a high impedance type (multimeter or testlight with a low power bulb or LED).

The circuit path in such a case would be through the other bulb(s) in the circuit, the ground side of the circuit, your tester and to ground. Because your tester has much higher impedance than the bulb(s), the largest voltage drop will be across it, hence the tester lights up and the bulbs don't.

Regards,
--
Kári in Iceland
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