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2021 1500 136 HR Iowa
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Discussion Starter · #1 ·
We have 2 LED bars under our cabinets on a circuit by themselves that will turn on with no fuse in the box. No other circuits act like this.

I’ve checked the voltage on the positive and negative terminals for this circuit with the fuse pulled, and it reads @3V. With the fuse in, it reads the expected @13.4V. No other circuits show voltage when their fuses are pulled.

We grounded the DC system to the B pillar with copper lugs and washers. At first I suspected a ground loop, but now don’t know what to think, since the problem only occurs in this one circuit. Wouldn’t a ground loop affect all circuits equally?
 

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I'm assuming 3V doesn't make them very bright. It does sound like that 3V is bleeding into just that one circuit. If it's not a short or ground loop, maybe it's induction from neighbouring wires. I've read that running 12VDC wires right alongside hot 120VAC wires can do that. Or it could even be a bad fuse holder. Where exactly did you take the 3V reading? Try at the fuse holder itself.
 

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2021 1500 136 HR Iowa
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Discussion Starter · #3 ·
I'm assuming 3V doesn't make them very bright. It does sound like that 3V is bleeding into just that one circuit. If it's not a short or ground loop, maybe it's induction from a neighbouring wire. I've read that running 12VDC wires right alongside hot 120VAC wires can do that.
You’re correct that they are quite dim when the fuse is not installed. We don’t have 120 yet. We have a 2000 watt inverter, but I want to run this to ground (no pun intended) before we bring that side into the equation.

It’s not likely that one other 12VDC line running up the same box would induct that one circuit, is it? The other line powers a cigarette lighter socket, a USB port, and a switch for the ceiling puck lights.
 

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2019 Promaster 3500 Silver high top 159"
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163 Posts
Uh, sounds like your circuit might be shorted or mis wired with something else. If you read 3v with the fuse pulled, then it is not open, it is connected to something... Figure out what that is and you'll solve your problem.

Correct me if I am wrong but gound loops have nothing to do with this. If the (+) supply is cut, there is no ground loop since there is no circuit. See above.
 

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2018 136" HR
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644 Posts
Are you using this type of chinese made fuse block?

I use similar one and other reviewers have said that even with fuse pull some voltage will flow through the red led. The only way to fix that is to remove the red led light connection in the back of the fuse block.
 
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2021 1500 136 HR Iowa
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15 Posts
Discussion Starter · #9 ·
Are you using this type of chinese made fuse block?

I use similar one and other reviewers have said that even with fuse pull some voltage will flow through the red led. The only way to fix that is to remove the red led light connection in the back of the fuse block.
Our block is bigger, but yes. A friend suggested the same cause last night. The red LED means a trickle current flows even without a fuse. I don’t really mind the issue, as long as it was not a mistake on my part. Thanks for the advice, everyone! This is a great forum.
 

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2017 2500 HiTop 159 Cargo Van white.
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706 Posts
I think a diode at the red led would keep power from back feeding. Something like that. I have a neighbor that is way smarter than me that figures out weird stuff like this for me.
 
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