DIY Auxiliary PDC/Fuse Box

This isn't as much of a how-to as it is just drawing attention to an interesting project I did. My understanding of electrical work has always been a little foggy beyond just being able to follow instructions. I have a few plans to add OBA, lights, etc to the Jeep sometime in the future. One of my big hurdles is that I don't want to create a rat's nest of wires, splices and connectors. I also wanted a better understanding of what was happening inside the factory Power Distribution Center (PDC) and attempt to mimic that.

Earlier this year, Bleepin Jeep did a video on building your own relay and fuse box by re-wiring an XJ PDC. This is essentially the box that I built, following Matt's instructions. He explains it far better than I ever could.


The main thing I wanted to point out is that XJ, ZJ and TJ PDC's are all very similar. While the outer cases are different, they all utilize the same interchangeable modules to create many different combinations of mini fuses, maxi fuses and relays. Different sets of modules are available within a model or trim package depending on the factory options. There seemed to be 8-10 different modules and 3-4 different cases, so look at every vehicle to find what works best for you.

WKdeuce made the following thread where he reconfigured the stock box on his XJ by switching out these different modules.
http://www.jeepforum.com/forum/f11/bens-you-already-have-relay-box-relay-box-1296952/

From WKdeuce's thread, here is one of the modules.


Combining these two ideas, here is what I came up with.

I began with a PDC from a salvage yard XJ.


There are several versions available depending on the year and the factory options. I chose this one because it would fit nicely next my my TJ's box. Understand that I have room here because I moved the stock air box a while back.

As mentioned in the video, cut the wiring harness as far back as you can so you can reuse as much of the stock wiring and connectors as possible. I also made sure to grab a second wiring harness with connectors. My box was made almost entirely of savaged wiring and connectors with the smallest wiring being 12 gauge.

Some shots of the build process...

This is tedious work, but it is as easy as following the wiring diagram and being systematic with connecting one set of terminals at a time.

Using modules from various XJ's and ZJ's around the salvage yard, I configured my box to contain 7 relays w/ maxi fuses and 12 mini fuses. It could have had an additional 7 maxi fuses if I had known to scavenge the needed clips to connect the fuses to the power block inside the PDC case. However, I can't imagine why I would need even more power connections.

Just as in the video, I added a bank of terminals to the outside of my box. Except for two big 8 gauge leads, each relay and mini fuse is connected to a terminal. Adding an appliance is as easy as attaching it to the appropriate terminal and adding a switch to the signal wire.


The relay signal wires are made from an ethernet cable I stole from work. I found one that used stranded wire instead of solid. Notice that a piece of signal wire is fitted into one of the seven relay terminal. These are labels so I know which relay belongs to which signal wire.

For my installation, I put the new PDC next to the stock box.

After cutting the legs off of the XJ bracket, I was able to bolt the new box to the inner fender using an existing hole.


Here are the insides,


I have about $40 in this fuse and relay box totaling 19 connections, about the same cost as the smaller capacity 12 circuit Blue Sea fuse box that does not contain any relays.