DIY Jeep Wrangler JK Waterproof Accessory Fuse Box

Jeep JK Waterproof Aux Fuses

If you own a modern Jeep Wrangler – YJ, TJ or JK, chances are at some point you’re going to want to add a light bar, bumper lights, winch, CB radio, aftermarket stereo or some other accessory that will need additional fused power. This DIY add-on fuse box example shows how you can run two separate sets of fused switches (or up to 6 fused circuits total) for an LED light bar on a Jeep Wrangler Unlimited JK, but really this example will work for any Jeep or 4×4. This DIY waterproof auxiliary fuse box can be set up for up to six fused accessories and can be built for less than $50 in parts and in about one hour.

Waterproof Box Jeep JK Auxiliary Fuse Panel
This waterproof auxiliary fuse box can be built for any application for less than $50 in materials. Shown here in a 2014 Jeep Wrangler JK Unlimited used to power auxiliary lighting.

 

The biggest obstacle I had with the JK Wrangler was there’s very limited space under the hood for additional accessory wiring. The only sizable gap I could find was directly on top of the battery. I measured the space and searched for a waterproof box of similar size and came across a BUD Industries waterproof economy box which measured roughly 10.5″ long by 4″ wide by almost 3″ tall. This is a nearly perfect fit for on top of the Jeep Wrangler JK battery, but also a nice size to mount to a firewall or fender for other Jeep Wrangler models or 4×4 applications. Best part is it costs less than $15 and is of very nice quality.  I chose to spray paint the box black so it would blend in better under the hood, but it comes in the grey color shown in the photo.

BUD Industries Waterproof Plastic Box
This Waterproof box from BUD Industries is a perfect fit to add a supplemental fuse block on top of the battery in a Jeep Wrangler JK.

Going off the internal dimensions of the waterproof box which are provided via detailed CAD drawing at Amazon I selected a six blade fuse panel for all of my positive wires that would fit well in the box and still leave room for relays, negative grounds and possible future expansion. I chose this six fuse panel with LED indicator lights to show if a fuse is blown/bad. The other nice part of this terminal is, like the waterproof box, it’ll cost you less than $15. The LEDs provide an easy way to see if you’ve got dead fuses without actually having to go through the box and pull each one to look. There are cheaper panels without LED indicators or a cover if you so choose.

This fuse box was capable of 100 total amps or 30 amps per circuit. Obviously at 30 amps per circuit multiplied by six circuits you cannot wire each one to maximum or you’d exceed the 100 amp maximum rating. For the lights I was wiring I only needed one 15 amp and one 10 amp fuse – leaving 4 positions open for future electrical add-ons. I wired 5 of these LED lights at 51 watts each on two different switches. To determine amps you need to divide the watts by the voltage. Each light was 51 watts, so three lights on one circuit equals 153 watts divided by 12 equals 12.75 amps. Two lights on a separate circuit equals 102 watts divided by 12 equals 8.5 amps. To wire the panel you simply run one lead (I used 14 gauge red wire) to the primary terminal (shown in photo below, post with nut on center right portion of the block) direct from the positive battery terminal. Plug the appropriate standard blade fuse in, then run off the positive pose back to your lights/winch/CB or whatever you’re powering.

6-Way LED Blade Fuse Box Terminal 100 amp panel 30 amp circuits
This fuse panel has LEDs to show a dead fuse as well as cover for labeling what fuses lie underneath.

For grounding I mounted a simple four terminal bus (also called a minibus or busbar) and ran a black 14 gauge wire from one terminal direct to the the negative battery post. That left three posts open for terminating negative grounds for any application you might need, including my lights. Once again, this is a less than $15 part from Amazon.

100 Amp Common MiniBus BusBar
Four terminal minibus for attaching ground wires. Another $15 part from Amazon.

I mounted all of the components – fuse block and bus bar – in the waterproof box. I used small hex head screws with nuts and rubber washers to secure them in the box. Next I drilled 1/2″ holes in the box and fitted it with waterproof plastic cable glands to keep it watertight where the incoming positive and negative wires enter and exit the box. I noticed over time the cable glands have a tendency to loosen up and need re-tightening. It might be a good idea to hit them with a little silicone, caulk or even a tiny bit of blue loctite to keep them snug.

In the picture below you can see the negative wire leaving the waterproof box through the bottom gland and linking directly to the negative battery post. I mounted the minibus on the same side as the negative post to keep a nice short run. Likewise the fuse block terminal is mounted on the opposite (top) side and you can see the 14 gauge wire running directly to the positive battery terminal through the top gland. The three middle glands serve is the inputs for the auxiliary lights served by two different switches and a pair of relays.

Waterproof Jeep JK Aux Fuse Box Wiring
Here you can see the hinged side of the box with 1/2 holes drilled and cable glands in place.

 

Waterproof Circuit Box Mounted in Jeep JK
I used industrial strength velcro strips to secure the box to the battery. The box is easily removed and set aside (leave slack in your wires) to pull the battery as needed. The Two hexhead screws on top are securing the relays to the top of the lid.

 

Waterproof Aux Fuse Box on top of Jeep JK Battery
The waterproof box provides a nice finished, almost stock look under the hood when done.

 

Jeep JK Waterproof Aux Fuses Light Relays Mounted to top of Waterproof Box Waterproof Box Jeep JK Auxiliary Fuse Panel  MiniBus Negative Ground Terminal Jeep JK

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