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Old 02-01-2019, 09:43 PM   #1
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Tail lights work intermittently

I have a 2002 Thomas e450 short bus. The tail lights, marker lights and the school bus cluster all go off then come back on. Sometimes they will shut off for a second sometimes for an hour . They will do this sitting still or while driving.

You can hear the relay click when they go off and click when they come back on. All other lights stay on when this happens. It also looks like the tail lights were replaced recently. They are a square shaped with two lightbulbs one on bottom and one on top. The top one never comes on.

I understand household electric( to a certain degree) but I've never dealt with auto. I'm assuming my problem is a short before the relay. How would I go about finding it? How does the wiring run? If anyone has any advice or tips I would greatly appreciate it.
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Old 02-01-2019, 09:54 PM   #2
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I have a 2002 Thomas e450 short bus. The tail lights, marker lights and the school bus cluster all go off then come back on. Sometimes they will shut off for a second sometimes for an hour . They will do this sitting still or while driving.

You can hear the relay click when they go off and click when they come back on. All other lights stay on when this happens. It also looks like the tail lights were replaced recently. They are a square shaped with two lightbulbs one on bottom and one on top. The top one never comes on.

I understand household electric( to a certain degree) but I've never dealt with auto. I'm assuming my problem is a short before the relay. How would I go about finding it? How does the wiring run? If anyone has any advice or tips I would greatly appreciate it.

the first thing I'd check is the ground
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Old 02-02-2019, 04:32 AM   #3
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Thanks. Turns out the tail lights have plastic housings and there isn't a ground wire anywhere.
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Old 02-02-2019, 11:12 AM   #4
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Please post some pics of the lights and wiring.


The noise you hear is more like a breaker tripping, no relays involved.


Each light socket must have a ground that is common and connected to each socket then the final ground connection could be hidden somewhere else in plain sight.


Without testing you won't learn anything looking at this problem.


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Old 02-02-2019, 03:59 PM   #5
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https://www.flickr.com/photos/162861...posted-public/
https://www.flickr.com/photos/162861...posted-public/
https://www.flickr.com/photos/162861...posted-public/

The white wire runs from the top ( non working) light down to the bottom and out thru the back. It gets no power. The other two wires are brake and running lights. As of right now they are both working. They both are getting 12 volts. The light housing is screwed into fiberglass on two of the bolt holes and the third runs thru the fiberglass and steel it had a washer on it and if I test there it's getting ground.
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Old 02-02-2019, 04:34 PM   #6
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The pic of the rusty hardware is not conducive to good grounding, so they need to be in as new condition first. The pics don't help much but maybe the ground goes all the way back to the switch for those light then to ground.
Maybe not but still a possibility.
The connection using mounting holes for grounding on fiberglass is most likely the culprit. Make a new ground point on the chassis somewhere close and try the operation of the lights. If they stay on make it permanent.


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Old 02-02-2019, 05:01 PM   #7
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Will do thanks
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Old 02-02-2019, 05:28 PM   #8
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So when multiple lights go out, in my experience, it's likely the ground wire. This is especially true if intermittent. Wire is likely drifting around and finally resting against metal when it is working.
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Old 02-02-2019, 06:14 PM   #9
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So what is the best way to ground these out? They are plastic housings. Should I run a wire to the socket?
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Old 02-02-2019, 06:29 PM   #10
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So what is the best way to ground these out? They are plastic housings. Should I run a wire to the socket?

Each socket will differ in number of wires.

Some 2, some 3 wires, one is ground in plastic crap.

One should be ground for that fixture. Simple test tells that.
Do the same for every socket then connect all the ground wires to your eventual newly installed ground wire.
Hope you know how to make a good connection for each.


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Old 02-03-2019, 09:14 AM   #11
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The studs (bolts) on these style lights are often used as the ground , and there is likely a slot in the back if each requires a wire. Self drilling screw (go with 1/4" hex head), attaching to the vehicle metal will assure proper grounding. Not the ideal tail light for a bus. Consider others set into the metal with rubber gaskets , oblong, and LED. Hole saw to drill each rounded end, and grinder with a cut off disk to remove the center to install.
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Old 02-03-2019, 12:22 PM   #12
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"It also looks like the tail lights were replaced recently. They are a square shaped with two lightbulbs one on bottom and one on top. The top one never comes on."

Looking at the pics, the new lamps may have been meant for a vehicle that has separate brake lights and directional lights---does the top lamp light when you turn on the directional signal? How about when the 4 way flashers are on? The ground is coming to each bulb via the steel backing plate. Attach a jumper wire from a known good ground to the plate and try all the lights. If they work you have isolated the problem.
Jack

P.S. If the bus doesn't have separate stop and signal lamps the top bulb will never light because the bus wiring doesn't exist to service it.
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Old 02-04-2019, 01:16 AM   #13
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These are the lights that were installed.

https://www.zoro.com/grote-stopturnt...72/i/G3286017/

When we bought the bus I figured they were the original tail lights. There not circle but I figured it was a shorty so they were different, untill I started paying attention to the other short busses around here.

The top lights do not come on at all but they were wired to something. The wire runs down to the bottom light grommet where the other two wires for the brake and tail lights run out of the back of the fixture. They are all together and run up the wall above the emergency exit and then I loose them. The top bulb gets no power. Out of the three bolts on the back only one was going thru metal the other two are going thru fiberglass ( maybe another problem I wasn't aware of).

Can I run a screw to the body and ground out each bolt on the back individually to make a better ground.

The only reason I'm wanting to keep these light is because they have a clear window on the bottom that lights up our liscense plate. The liscense plate lights were also removed along with their wiring.

They're also working great right now so that's not making it easy.
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Old 02-04-2019, 09:00 AM   #14
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Have you checked for backup lights on the one that you seem baffled by?


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Old 02-04-2019, 02:23 PM   #15
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Yes and nothing. We do have separate back up lights and separate blinkers that work fine.
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Old 02-04-2019, 04:15 PM   #16
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The clear section of that type of taillight is for reverse lights. This is not the original equipment taillight for any (school) bus that I have ever seen. The bulb that you are saying is not wired up is for the reverse light.
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Old 02-04-2019, 07:27 PM   #17
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The clear section of that type of taillight is for reverse lights. This is not the original equipment taillight for any (school) bus that I have ever seen. The bulb that you are saying is not wired up is for the reverse light.
Those lights usually come in pairs, one with a clear lens on the BOTTOM for the license plate and a small clear lens on the face for back up light. They can be purchased separately with or with out the license lens.
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