Nucamp 400 Fusebox red light won’t turn off?

riverchemistry

Noticed the red lamp on my interior lights it reads doesn’t turn off. At first I thought it was a bad fuse, swapped fuses and still lit up. Interesting is, when I remove the fuse it lights brighter than it is. And returning the fuse it dims. Other fuses when removed light up bright and turn off when returned. Anyone have insight on this?

MuttonChops

Take a look at this thread
'Fuse Keeps Burning Out'  https://tab-rv.vanillacommunity.com/discussion/13210/fuse-keeps-burning-out 

Depending on what your Fuse-2 is connected to it is most likely a false fail indication due to minor current leakage.

davel4wa

All of the bizarre DC circuit behavior described here was blowing my mind. It occurs to me that all of this is related to one thing. The 'blown fuse' indicators in fuse blocks are made in the cheapest possible fashion. That is that an LED is connected in parallel with the fuse, either with an internal or external resistance. This means that if the fuse is blown or removed the 12vdc current path is through the LED causing it to light. Unfortunately, this can be confusing if you are measuring the voltage at the device (light, usb port, refrigerator, etc) with a high impedance device like a VOM (volt-ohm-meter). Because the 'blown fuse' indicator LED is completing the 12vdc circuit, your VOM will measure 12v present. The way around this is to make sure there is a load connected where you are measuring. This will insure that all or most all of the voltage will be dropped across the 'blown fuse' indicator so that your VOM will read less than and likely closer to zero depending on the current through the circuit.
The better solution, of course, would be for manufacturers to stop using this cheap and dirty indicator method. An inexpensive logic circuit embedded in the fuse block would provide the desired indicator function without providing the sneak current path provided by the inline indicators now being used.
Just sayin'

Grumpy_G

Stuff like this intrigues me so I had a close look at the fuse center. Indeed there is a row of three resistors connecting the feed side to a LED that in turn connects to the protected side. As @davel4wa wrote when the fuse blows *and* the load is still turned on (or the short present) the LED lights up. But that also means if there is no short and the load is turned off or the fault caused it to go open the LED doesn't light up. I confirmed that by pulling the fuse for the 3 way fridge. Fridge off=LED off, Gas=LED on, AC=LED off, DC=LED on. Way to confuse people ! 

As for the OP, normally the resistance across the fuse is much lower than across the resistors and LED. So either there is a bad solder joint at the fuse holder, or one of the resistors is wrong (total across all three measured 2k) and makes the LED glow a bit. 

MuttonChops

@Grumpy_G ; Like your ideas . . . .
Historically these false fuse failure LED situations are caused by the USB Ports.  The USB Ports are (also) made cheap and frequently outright fail or leak current when not-in-use enough to light the LED.