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Old 08-29-2021, 03:17 PM   #1
ctg
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2021 27' Flying Cloud
Modesto , California
Join Date: Oct 2015
Posts: 7
Blowing the 7.5 amp fuse

We have a 2021 Flying Cloud. After 1 year of use it blew the 7.5 amp fuse that controls the main cabin lights among other lights. When I replace the fuse it immediately blows again. Has anyone run into this? Logical place to begin the troubleshooting? Thanks
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Old 08-29-2021, 05:54 PM   #2
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Hi

You either have:

1) A wire shorted to ground

2) A blown light fixture

3) Something else patched into the circuit.

You should know if you have added anything and be able to cross number 3 off the list ( or go look at what you added).

There is no *simple* and safe way to sort out 1 and 2. It's simply a matter of doing this and doing that.

First, grab your multimeter and see what the resistance to ground is. If it's something really low ( like a couple of ohms) that suggests number 1 is the better bet ). If you get a fairly high reading (> 100 ohms) that suggests number 2. In-between ... who knows.

Next, pick a light fixture that is close to the switch and pop it off the ceiling. You should find wire nuts behind it. If so unscrew the one on the hot lead. If you have crimp connectors .... sorry about your luck. The drill is the same, you need to break the circuit.

Once you have the first point "open" check the resistance again. If it went from one ohm to a thousand ohms, the problem is past the point you just pulled open. You can try a fuse to demonstrate this.

Once you have ruled out a fixture it gets jumped back in. You don't really *know* the order so you may revisit this or that fixture.

You keep chugging through the fixtures doing this. At some point you will get to or past the problem. When you do, you pop off the fixture. If all is well with "that fixture" out of the group .... you have the culprit. If all is well with "that wire" out of the group .. same thing.

Since this is a "rule it in / rule it out" kind of thing, you may pop out all the fixtures before it's all sorted. That's just part of the process.

Not a lot of fun, but not crazy hard to do.

--- or ----

Drop all the fixtures first and look for signs of parts melting down. If you find a future that looks "cooked" pull it and see what happens.

Bob
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Old 08-29-2021, 07:38 PM   #3
ctg
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2021 27' Flying Cloud
Modesto , California
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Posts: 7
Blown fuse

Thanks for the direction.
Will be a good project to start on tomorrow night......
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Old 08-29-2021, 08:12 PM   #4
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A simple trick to help find a short quickly-remove the wire from the fuse and wire a 12V lamp socket in series-one wire to the fuse and the other to the wire you just took off the fuse. Put a 12 volt incandescent lamp in the socket and insert a new fuse, it will not blow. The test lamp you just installed will glow brightly because it is getting power from the fuse and ground from the short. The lamp limits the current so the fuse will hold. Start taking stuff apart or jiggling stuff, I like to try and guess where the approximate middle of the circuit is and separate it there which tells me which half has the short, then split that half etc till you narrow it down. When the test lamp dims or goes out you have disconnected the short. Sometimes it will go out but if there are other loads like lights switched on the test lamp will still glow but not as bright as the loads will have resistance and are in series with your test lamp. The more loads the brighter the test lamp so try and have all your switches off.

I have done this many times with house AC wiring as well and it enables us to drill down to the location of the short very quickly which always amazes the customer who spent days taking stuff apart and poking into everything before calling us.

The other tip is look for the obvious, any screws been recently installed? BTDT. Also turn off all switches, it may point to the fixture or wire run that is shorted if the short goes away with the switch off. Also, if the switch is off to a fixture and the short still exists you know it's not that fixture causing it so don't waste time pulling it (provided that the positive wire is the switched one). Switches can move around too and short against the metal, fixture screws can be driven right thru a wire.

I can't stress how important is is to turn off all your switches, that simple act could find the short very quickly. BTDT
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Old 08-30-2021, 10:39 AM   #5
DentsAndFiliform
 
2018 26' Flying Cloud
Wilsonville , Oregon
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For what it's worth, we had a problem on a circuit that kept blowing a 15 amp fuse. Turns out one of the wire bundles from the lower wiring tunnel that comes up into the trailer was not loomed properly (too short). One of the wires, a blue one, had rubbed through on a baffle causing an intermittent short. After fixing the wire and looming the bundle, the short was fixed. This particular short killed our ceiling fans, bathroom lights and thermostat. This wire bundle came up through the floor under our closet next to the water pump. You might want to take a quick look just to make sure you don't have the same problem.
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Old 08-30-2021, 04:42 PM   #6
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Lady Lake , Florida
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Testing

You can take the blown 7.5 fuse out and then use a hand held DVOM meter set to 10 amps scale .

Make a test wire with a terminal that fits in the fuse box and and have a 10 amp fuse wired in series , So one side of the 10 amp fuse is plugged into the 7.5 amp empty terminal. They using your DVOM set to 10 amps clamp to the 10 amp fuse wire and complete the circuit with the other meter terminal to the other removed fuse terminal. Your amp meter is in series of the removed fuse. The 10 amp fuse is a safety to your meter it blows before the meter fuse blows.

Then turn on one set of lights at a time watching the current draw. The set that blows the fuse is the culpret. If it all sounds confusing PM me.
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Old 08-30-2021, 05:24 PM   #7
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Quote:
Originally Posted by Life is a Highway View Post
You can take the blown 7.5 fuse out and then use a hand held DVOM meter set to 10 amps scale .

Make a test wire with a terminal that fits in the fuse box and and have a 10 amp fuse wired in series , So one side of the 10 amp fuse is plugged into the 7.5 amp empty terminal. They using your DVOM set to 10 amps clamp to the 10 amp fuse wire and complete the circuit with the other meter terminal to the other removed fuse terminal. Your amp meter is in series of the removed fuse. The 10 amp fuse is a safety to your meter it blows before the meter fuse blows.

Then turn on one set of lights at a time watching the current draw. The set that blows the fuse is the culpret. If it all sounds confusing PM me.
It sounds confusing to me and I'm an electrician! If the fuse would hold with all the lights turned off and blow when only one was turned on why would you need to hook up all that other stuff? Why not just replace the original fuse and start turning things on till you find the one that blows the fuse?
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Old 08-30-2021, 11:28 PM   #8
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Yes

This would be so you could watch current flow as you added loads or watch to see if and when it blew. I’ve had to do this in automobile fuse blocks watching current change in cold the warm loads such as with solenoids or fuel pumps. Anyway resistance is going down causing them amps to go up. If it’s a instant blown fuse.
Other options is to start start looking on back of the fuse box and electric panels. Could be a light switch shorting or a light hot wire touching ground

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Originally Posted by ITSNO60 View Post
It sounds confusing to me and I'm an electrician! If the fuse would hold with all the lights turned off and blow when only one was turned on why would you need to hook up all that other stuff? Why not just replace the original fuse and start turning things on till you find the one that blows the fuse?
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Old 08-31-2021, 08:01 PM   #9
ctg
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2021 27' Flying Cloud
Modesto , California
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Fuse

Thanks for all the helpful responses. I think we may have found the issue. Our shower fan is faulty and not spinning. Will be replaced this weekend. More to come.
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