Wednesday, November 29, 2023


RV Electricity – Just Ask Mike (J.A.M.): Blown fuse indicator

By Mike Sokol

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) with the subject line – JAM.

UPDATE: What cost, Electricity?

Join me Sunday, December 1, for my latest RVelectricity newsletter where I discuss everything about the price of electricity, including what it costs a campground to provide shore power for your RV around the country, portable space heater costs and safety updates, and the future possibilities of EV RVs (ERV?) beginning with the upcoming Volkswagen I.D. Buzz. I’ll even begin discussing EV Toads and how campgrounds might respond to having you plug your ERV or Toad into their pedestal for charging. Subscribe to this (and other) newsletters HERE. —Mike

Dear Readers,
Last week, one of my astute readers reminded me to remind you about this cool gadget. It’s a replacement blade fuse for your RV’s 12-volt DC panel that will turn on a little LED light when it blows. That’s right, when all is well there are no lights in the fuses of your power panels. But if a 12-volt DC fuse blows (for whatever reason), and if the battery power is still on, then you’ll get an indicator LED light lit up on the offending fuse.

How does it work? Glad you asked. When the fuse is good it’s essentially shorting out the little LED indicator light and it can’t come on. However, when the fuse blows, it opens up and allows the LED light to draw a tiny bit of current from the shorted circuit that blew the fuse in the first place. And that’s enough leakage current to cause it to light up and tell you where the blown fuse is located. So: No light = good fuse. On light = blown fuse.

While this sort of indicator light is built-in on some DC fuse panels, you can easily upgrade your regular fuse panel to the LED indicator types for a few dollars. Just be sure you match the fuse amperage to the circuit requirements. So no cheating trying to put a 20- amp fuse in place of a 5- or 10-amp fuse.

You can find these LED indicator fuses in many auto parts stores, or you can buy a pack of them in a variety of amp ratings from Amazon HERE.

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….



Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.

##RVDT1218;##RVT 924



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Brian Richards (@guest_60596)
3 years ago

As Sargeant Shulz used to say on the old tv show…….”Very interesting!” That is such a cool product. I did look on the Amazon site and they are out of stock, don’t know when they’ll get more in. Ouch!

John T (@guest_57597)
3 years ago

You did not mention that for this thing to work, the electrical appliance in the circuit must still be switched on. If it is switched off, there is no complete circuit to light the LED.

STEPHEN P Malochleb (@guest_57543)
3 years ago

Thanks Mike, After reading last weeks article I ordered 2 sets to put in the rig. I am very good with a DVOM but this makes life easier….

Clayobx (@guest_57492)
3 years ago

We have been using and replacing all our DC OEM fuse’s for the past few years. They work and save time if a problem jumps up. I also find the quality of Carax product greater than the original supplied. Certainly a thumb’s up product.


Jerry Murri (@guest_57491)
3 years ago

This is a good idea, but can you buy them individually? My rig uses 15, 20, 30 and 40 amp fuses. Just want the ones I need.

John T (@guest_57595)
3 years ago
Reply to  Jerry Murri

You can use it in any circuit. It’s not a fuse, it’s a light. The rating of the circuit is not relevant.

John T (@guest_57598)
3 years ago
Reply to  John T

Ignore my last comment. At first reading, I thought it was a test light, not a replacement fuse.

Steven I Bennett (@guest_57224)
4 years ago

I would like you to discuss about mini split air conditioning and heaters being installed in RVs what are the difficulties what are the costs do they hold down AC related expenses etcetera thank you

Alvin (@guest_57214)
4 years ago

Mike thanks a million for this one. I have a tendency to look in on things that make me smarter – I guess the older you get the less time you realize you have to get smarter so…… This tip made me a lot smarter in seconds – great value here thanks again, I’m putting these indicator light fuses on my list. Alvin Shier

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