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post #1 of (permalink) Old 06-12-2004, 06:49 PM Thread Starter
 
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Brake light troubleshooting - SOLVED, thanks!

Okay, electrical guys... discovered this afternoon that my brake lights are not working on my 87 YJ, courtesy of the local constabulary. [img]images/graemlins/blush.gif[/img] Now I need a little help troubleshooting. Here's the situation:

1) Tail (parking) lights, back-up lights, turn signals, and hazard lights all work fine - both sides.

2) Hooked up a digital voltmeter to the brake light switch (on the pedal lever). The switch shows infinite impedence when the pedal is up and <1 Ohm when the pedal is down (resistance of the test wire). I'm assuming this indicates the switch is working - I didn't find a reference in my Haynes.

3) A four prong (3+1) trailer light plug is spliced in to the harness right in front of the plug in the hard top for the dome light (above driver's tail light). All trailer lights (parking, brake, turn, and hazard) have worked fine until now.

4) Brake AND parking lights have quit working on the trailer. Turn signals and hazard lights still work fine on both sides.

5) Hooking up the trailer lights has no impact on the behavior of the <nobr>Jeep's</nobr> lights.

6) The fuse box shows that the hazard and brake lights are on the same fuse. Checked it anyway and it's good.

Any help would be most appreciated. [img]images/graemlins/smile.gif[/img]
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post #2 of (permalink) Old 06-12-2004, 07:18 PM
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Re: Help - brake light troubleshooting

First you need to check for power to and from the brake light switch. You should be able to back probe the connector. If you can't get your meter probe in there, unbend one end of a paper clip or find some other small diameter stiff wire to use as a probe.

I'm assuming that '87 uses the same bulb for brake/turn/hazard. If that's true, the next place to check is the connector at steering column. There are switches in there that interrupt the brake signal for the turn or hazard flashers. You'll need a schematic to determine which pins to check. If the brake signal is going in but not coming out to power the bulbs, you've got a bad turn/hazard switch.
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post #3 of (permalink) Old 06-12-2004, 07:20 PM Thread Starter
 
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Re: Help - brake light troubleshooting

UPDATE - Just went out and happened to be looking toward the back of the Jeep when I bumped the brake pedal and saw the brake light flicker. If I just barely touch the brake pedal, the brake lights come on. But as soon as I apply any decent pressure, they go out. Stepping on the brake doesn't even give them enough time to flicker.

When I tested the switch with the voltmeter earlier, I was actually stepping on the pedal. Does anyone know what the impedence should be when the pedal is pressed?
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post #4 of (permalink) Old 06-12-2004, 07:43 PM
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Re: Help - brake light troubleshooting

</font><blockquote><font class="small">In reply to:</font><hr />
When I tested the switch with the voltmeter earlier, I was actually stepping on the pedal. Does anyone know what the impedence should be when the pedal is pressed?

[/ QUOTE ]

I would guess very low near 0 Ohm... but maybe better to help understand what is happening... put the meter on DC Volts, gound the black lead to the body and check the switch while pressing the brake peddle. You should see battery voltage as soon as the switch makes contact and remain there until it opens back up. Seems like you have a mechanical issue with the switch it's self or maybe just a flaky switch.

Another thought, jump across the switch and be sure that the brake lights come on and stay on.

Gook Luck

Dale
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post #5 of (permalink) Old 06-12-2004, 08:29 PM
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Re: Help - brake light troubleshooting

that switch by the pedals... should be an open or 0 volts when you are not pressing on the pedal.. when you do press on it... it should read close to 0 ohms... or 12 volts..
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post #6 of (permalink) Old 06-12-2004, 09:03 PM
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Re: Help - brake light troubleshooting

</font><blockquote><font class="small">In reply to:</font><hr />
If I just barely touch the brake pedal, the brake lights come on. But as soon as I apply any decent pressure, they go out.

[/ QUOTE ]

I'd say change the switch. For simplicity (and to make them inexpensively), some switches use wipers. It slides one contact onto the other rather than pressing one contact into the other. That momentary ON then back OFF is typical of them when they go bad. One of the wipers gets bent or breaks off.
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post #7 of (permalink) Old 06-12-2004, 09:12 PM Thread Starter
 
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Re: Help - brake light troubleshooting

</font><blockquote><font class="small">In reply to:</font><hr />
Another thought, jump across the switch and be sure that the brake lights come on and stay on.

[/ QUOTE ]

That did it... the problem is in the plug connector. Jiggling the wires with the leads jumpered causes the lights to flicker. I'll be replacing the connector tomorrow. Now it's time for pizza, beverages, and a movie. [img]images/graemlins/smile.gif[/img]

Thanks for the help, guys. [img]images/graemlins/40BEER.gif[/img]
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post #8 of (permalink) Old 06-12-2004, 09:20 PM
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Re: Help - brake light troubleshooting

It's the simple little crap that will kill you.

</font><blockquote><font class="small">In reply to:</font><hr />
Now it's time for pizza, beverages, and a movie.

[/ QUOTE ]

Excellent ! [img]images/graemlins/cool.gif[/img]

Beverages for me thanks. [img]images/graemlins/40BEER.gif[/img]

I always enjoy a problem that ends well.

Dale
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