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Old 10-28-2021, 09:08 AM   #1
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2015 27' FB International
Chapel Hill , North Carolina
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Internal light problem, possible grounding issue

I have a 2015 27FB International that weíve owned since new.

There is an intermittent issue with the 3 LED lights in the cabinet above the bed. More recently, these lights are often very dim when turned on. So dim in fact that itís hard to see that they are even on unless youíre looking at them close up, like a few inches away. Iíve measured the voltage to the lights at the light switch at about 7V (which explains why they are so dim). The switch itself is fine. Sometimes the lights will come on bright (but not as bright as they should be), and you can also notice that they flicker occasionally. This seems to me to be a ground issue in that particular light circuit. In retrospect, I think this subtle flickering has been going on for years, but never really got my complete attention until the lights very obviously werenít turning on and working right.

As an experiment, Iíve tried adding a ground wire to a negative connection at one of the lights in the cabinet. This seemed to have no effect, i.e. the light stayed consistently dim. (As this was a quick experiment, itís possible that my extra ground wire wasnít grounded well during this trial. I tried grounding to the aluminum shell and also the ground wire of the nearby 110V socket.)

Does anyone have any ideas on how to fix this? I have no idea where the ground point is for this circuit. Maybe the fault is on the 12V (positive) side of the wiring?

Thanks
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Old 10-28-2021, 06:17 PM   #2
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Run a temp +12V jumper wire from the converter to the switch. If the the lights come on normal you know the ground is good and you need to look at the feed wire.
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Old 10-28-2021, 07:23 PM   #3
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You likely have a broken wire, bad crimp, or loose ground screw. If those lights are wired piggy-back style (one feeding the next) then a problem on one will affect all those downstream.

There is no secret to fixing this. You've got to do a little hunting. If I was troubleshooting I'd pull the lights from their mount and peak behind to see the status of things. Not too far at first, since you don't know how much free play the wiring has. Same for the switch - the connections need to be explored for a bad connection.

Sometimes a crimped fitting can look good from the outside but only be holding on by a few strands of wire. As the wire pulls further and further out with fewer strands still connected you'll get voltage drop in the circuit. Same for loose or bad ground connections.
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Old 10-29-2021, 08:46 AM   #4
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Follow up...

Thanks for the feedback bel73 and richard5933. You made me realize that I didn't check the voltage to the switch properly. The voltage to the switch is indeed +13V, all good up to that point. However, the voltage drop is only about 7V when measured bypassing the switch, i.e. grounding through the lights. So, somewhere between the switch and the lights is a bad connection or the ground connection is bad for that circuit.

I pulled out the LED lights from the cabinet (see pictures) exposing the wiring (brown and white) as much as possible. All the connections there seem ok, at least visually. I also pulled/wiggled on all the wires at the connection points to see if that made any difference, to no effect. I also pulled off the speaker underneath the cabinet hoping I might be able to follow/access the brown/white LED wiring to within the cabinet with no success. (picture attached Ė the purple and black wires are speaker wires; any idea what the unconnected blue and white wires are? Just curious). The LED wires are not accessible or visible from the speaker opening.

Not sure what to try next. Is it possible that the problem could lie with one bad LED light?
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Old 10-29-2021, 09:28 AM   #5
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What are you using for a ground when connecting your meter?

If you have +13V coming into the switch and only +7V leaving, the switch is bad. You should only have the two wires on the switch. Take them both off the switch and connect them together and see if the lights come on normal. If they do it will confirm you have a bad switch.

You can also check the resistance of the switch. It should be 0 ohms.
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Old 10-29-2021, 09:37 AM   #6
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I disconnected the switch completely and measured the input voltage at the disconnected 12V wire, grounding to the Airstream shell (shows 13V). The 7V measurement is made without the switch, i.e. switch completely unplugged. In other words, if I manually connect the 2 switch wires (without the switch), the LED lights come on very dim (same as with the switch connected and on). The voltage drop between the 2 wires (without the switch) is 7V. The switch is fine.
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Old 10-29-2021, 09:40 AM   #7
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After you have checked the switch, fasten a wire to a good ground then poke the other end into the underside of the connector on one of the white wires at any of the 3 lights making contact with the metal splice, use a T pin if necessary or even a straight pin if you have no T pins. Do this with the lights ON and in the failure mode. If you have a bad ground this will make all 3 lights come up to normal brightness when your test wire/pin makes contact inside the connector.
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Old 10-29-2021, 10:05 AM   #8
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Thanks Brian. I tried grounding at the light, as you suggested. No effect. It then occurred to me to use the VOM to check the resistance at each negative light wire (grounding to the Airstream chassis). The resistance is 0 at each light, therefore the ground connections are all good. I also checked the voltage at each light. Each light shows 7.5V when on (same as at the switch). This seems to have narrowed it down to the 12V+ wiring between the switch and the lights. No problem with the negative side.

I'm again at a loss now how to pinpoint or fix the problem if there is a poor connection somewhere in the 12V+ wiring to the lights
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Old 10-29-2021, 10:06 AM   #9
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I'm guessing it's a poor connection on the +12V feed wire going to the switch. Not allowing enough current to pass and dropping the voltage.

Try what ITSN060 said. If that doesn't work try like I said before and grab a good +12V source and connect it to the switch.
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Old 10-29-2021, 10:13 AM   #10
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Thanks Brian. I tried grounding at the light, as you suggested. No effect. It then occurred to me to use the VOM to check the resistance at each negative light wire (grounding to the Airstream chassis). The resistance is 0 at each light, therefore the ground connections are all good. I also checked the voltage at each light. Each light shows 7.5V when on (same as at the switch). This seems to have narrowed it down to the 12V+ wiring between the switch and the lights. No problem with the negative side.

I'm again at a loss now how to pinpoint or fix the problem if there is a poor connection somewhere in the 12V+ wiring to the lights
Well you can do the same thing with a test wire this time from a 12 volt source to the black connector at one of the lights. If that doesn't give you full brightness then try disconnecting one light at a time to see if one of them is shorting enough to draw excess current )but not enough to blow the fuse) however unlikely this seems. By then you will have checked everything and should yield a result. Be careful not to accidentally ground out your 12 volt test wire anywhere.
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Old 10-29-2021, 10:45 AM   #11
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Thanks again Brian. I ran a test wire as you suggested from the light switch directly to the 12V+ connection LED lights. The lights (and switch) then work fine, full brightness. Sooooo, the problem definitely lies in the 12+ wiring between the switch and the lights. Not sure how to find the specific point of the bad contact now without tearing off some aluminum, which I won't do. Wouldn't be easy to run a new live wire either. Hmmmmm.....
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Old 10-29-2021, 10:57 AM   #12
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Thanks again Brian. I ran a test wire as you suggested from the light switch directly to the 12V+ connection LED lights. The lights then work fine, full brightness. Sooooo, the problem definitely lies in the 12+ wiring between the switch and the lights. Not sure how to find the specific point of the bad contact now without tearing off some aluminum, which I won't do. Wouldn't be easy to run a new live wire either. Hmmmmm.....
Time to get creative and do some thinking, you don't have to go directly from the switch to the lights, is there a round about way to get there. When re-wiring old houses many times we would run from a switch down under the house over to a chase then up to the attic to reach a light that otherwise would have meant plaster damage. It took a lot more wire but no plaster repair. Voltage drop won't be a concern with the light load you have there. Is there a partition wall near to one of the lights? any access by removing other fixtures or fan? I wish I were there, it was always rewarding to find a route to a fixture that didn't involve damage.
You could also add another light which would give you the opportunity to cut an access hole which the new light would cover.
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Old 10-29-2021, 11:12 AM   #13
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Yeah, I'll have to ponder this a while. I wish I knew exactly how/where the wiring runs under the skin, and where the junction points are (assuming there is a bad connection point and not just a fault within the wire itself). At least I have the problem narrowed down. Thanks again for your insight. Definitely helpful.
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Old 10-29-2021, 11:18 AM   #14
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Maybe one of the lights itself is misfiring and drawing too much current, causing a voltage drop. Can you test the lights one at a time?
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Old 10-29-2021, 11:31 AM   #15
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Thanks Richard5933. All lights (and switch) work fine when connected to a 12V test wire setup (discussed earlier). I also ran the test wire to each light further confirming everything works. Definitely a breach somewhere in the 12V+ wiring between the switch and the lights.
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Old 10-29-2021, 12:16 PM   #16
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Yeah, I'll have to ponder this a while. I wish I knew exactly how/where the wiring runs under the skin, and where the junction points are (assuming there is a bad connection point and not just a fault within the wire itself). At least I have the problem narrowed down. Thanks again for your insight. Definitely helpful.
Splices are normally located where accessible only having to remove fixtures etc. to access. If a wire is bad in the middle of a run it is normally from damage.
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Old 10-31-2021, 09:21 AM   #17
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Fixed...

It took some contortionist fishing but I was able to run a new positive wire from the switch to the rear cabinet lights. It wasn't exactly easy but I was able to run the wire along the ceiling duct to the rear cabinet. No cutting or any other obvious evidence it was modified.
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