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post #1 of (permalink) Old 10-12-2015, 11:45 AM Thread Starter
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Rear Lighting

We are having problems with rear lights. Initially both right rear lights were not working (tail and brakes). My son replaced both bulbs and now the top reverse light works and so does the break light. However, the normal tail light does not light. Using a volt meter we seem to be getting an inconsistent voltage sometimes a constant 9 to a jumping voltage from 7 to 11.5. Any suggestions on what to look for next?

We have installed trailer hitch wiring to this left rear connections (cannot test these lights as we do not own a trailer) but should I maybe disconnect the hitch connection and see what happens?

The search for "tail lights" had threads on CJ's, JK's, and trailers but other internet search talked about fuses (my son's search) so I could use some help.

Thanks,

Mark

2003 TJ

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post #2 of (permalink) Old 10-12-2015, 11:59 AM Thread Starter
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The hitch wiring works. After typing the question I realized I could test the electric at the 4-pin connector. Those pins have a constant voltage for the tail lights and brake lights.

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post #3 of (permalink) Old 10-12-2015, 02:24 PM
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First, testing for voltage with a digital multimeter is a dicey proposition. Typically they are so sensitive that they can pick up voltage where there's such great resistance that there's not enough power to do anything more than tickle the voltmeter. That's why you can get readings from 7 to 11.5 when there's nothing apparent to cause the fluctuation. You're generally better off to use a 12-volt test light. If there's not enough power to light the bulb you have nothing, despite what the meter might say.

Second, your problem is typical of that caused by bad grounds. My old Jeep has a connector at the driver's left foot that takes the harness to the rear along the side, behind the roll bar and to the rear of the left fenderwell. At that point it goes through a boot and to the left-side lights. The remaining cable goes from there through the back of the tub to the right lights.

At the point where the cable drops through the fenderwell is a screw into the tub that serves as a ground point for all the rear lights. If this were my Jeep, that screw would be loose or into rusted metal. Your Jeep probably has a similar ground point somewhere along the wire harness, and it's more likely inside the body than outside. And, being in the Great Salty North Country, it's probably rusty.

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post #4 of (permalink) Old 10-12-2015, 04:07 PM Thread Starter
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Behind the right rear wheel, there is a white wire with a green stripe screwed into the frame. This connection is a little corroded but not broken or loose.

Not being an electrician, aren't all the lights on the right all grounded through the same connection leaving the rear light harness?

Capture.JPG

Because the brake and reverse lights work on the right rear, I am still lost.

This is my first attempt to attach a picture, but this picture is from 8W-51-3 of the 2003 Service Manual.

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post #5 of (permalink) Old 10-12-2015, 05:25 PM
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Quote:
Originally Posted by Jim_Lou View Post
You're generally better off to use a 12-volt test light. If there's not enough power to light the bulb you have nothing, despite what the meter might say.

Careful there. Most of todays tests lights are LED. They will light up bright with low voltage. Its getting harder to find a old school light bulb test light. I have one of the new fancy led test lights with a volt meter built in. I have seen it show 12 volts and light the bulb, then use my old school test light and watch it drop out to nothing. The best test for this would be a volt drop test.

Unplug your trailer harness jumpers and see if there is corrosion in the plugs terminals. We see that all the time at work with are tractor and trailers. Nobody uses electrical grease when installing plugs and water gets in rots out the terminals. They will be green you can't miss it.

What????
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post #6 of (permalink) Old 10-12-2015, 11:36 PM
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I vote a ground issue.

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post #7 of (permalink) Old 10-13-2015, 09:51 AM
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Quote:
Because the brake and reverse lights work on the right rear, I am still lost.
Good point. That could be because the right and left lights have their own separate ground, or it could be some other issue.

And Pontiac is absolutely correct. To track down this type problem, where a DVM finds phantom voltages, you need an old-fashioned test light with a 12-volt incandescent bulb. It will draw enough current that the bulb won't light if there's high resistance in the circuit.

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post #8 of (permalink) Old 10-13-2015, 05:45 PM
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Quote:
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And Pontiac is absolutely correct. To track down this type problem, where a DVM finds phantom voltages, you need an old-fashioned test light with a 12-volt incandescent bulb. It will draw enough current that the bulb won't light if there's high resistance in the circuit.
This is too funny we are having this conversation. We had a customer trailer come in the shop today with no lights working on the top curb side. Our ace mechanic, that knows all (we all know the kind), went right after it with a led test light. I watched him change 3 lights on the side of this trailer and still couldn't figure out what was going on (its really painful watching this, but i am told to let it be). I finally couldn't take it any more and climbed up along side of him and put my old light bulb test light on his and wow no lights on any test light. Then looked over to the wire and found an old repair, grabbed ahold of the wire and pulled, out came nothing but green dust. I just had to tell this story, it had me laughing all day that i read this post last night.

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post #9 of (permalink) Old 10-13-2015, 07:32 PM
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sounds like a bad ground,you could use a jumper wire from a good known ground, (maybe scrape off a spot on the frame) and touch the other end to the bulb base.

How did I get sand THERE!
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