Auxiliary Fuse Block

As I move forward with the build-up, I know there will be a long list of 12V devices that will be added to the jeep. Rather than creating a rats nest by the end of the project, I decided to add a 2nd fuse box under the hood to kee things tidy. For added protection, the fuse block has a 70A cicruit breaker protecting it, and a 75A relay which only allows the fuse block to energize if the ignition is on.

In the future, I plan to connect the following devices:
- Laptop Computer
- 8" LCD Monitor
- 120V Power Inverter
- Back up Lights
- Back Up Camera
- LED Rock Lights
- Air Horn
- CB Radio

The winch/air compressor power plant I plan to install will be connected to the battery directly.

Originally, I was looking into Painless Performance's kits. The CirKit Boss®™ Heavy Duty Auxiliary Fuse Block caught my eye. However, it only has 7 Circuits so I kept looking.

I ended up purchasing a Blue Sea Systems 5026 fuse block. Its weather resistant and good for 100A of load. I purchased the fuse block from ProductShipMarine.com for $38.61.

Individual fuses protect each circuit. However, to protect the whole fuse block and wire to the battery, I installed a 70A circuit breaker.  I purchased the relay from ProductShipMarine.com for $36.

To make sure I don't leave something turned on and drain my battery, I installed a relay.  This basically is a switch which only allows power to flow to the fuse block when there is power from a second source.  The second source is the auxiliary 12V power outlet in the jeep (cigarrette lighter) since this wired such that it only has power when the ignition is switched on.  The reason you use a relay rather than wiring directly to the cigarette lighter is that the cigarette lighter has a tiny 18 guage wire feeding it.  It probably has a 10 or 15 amp fuse protecting it.  These are hardly sufficient for the amount of load I'll eventually be adding to the jeep.

Here is a look at the setup: (click on photo for full size image so you can read text):

At first I was confused about which terminals on the relay went to which thing.... after looking on the internet, I determined the correct wiring. 

Here is the relay I bought:

I bought it on ebay for $27.   I read somewhere you should mount the relay terminals down to prevent water leaking into the relay.

I decided to install the fuse block inside a plastic case to help keep water and dirt out.  I've seen some other people mount this fuse block on top of the lid to the jeeps fuse box.   The case I chose was a Polycase dc58f-g.  It cost $17 with shipping from polycase.com.

Finding a place under the hood of a JK for anything is tough.  This isn't a very big box, but trying to mount it somwher away from engine heat, excessive water, and accessible was tough. 

In the end, I chose the corner up by the master cylinder. 

I fabricated a small bracket that utilized existing bolts to mount the box to.

I mounted the fuse block inside the box, and then mouted the relay and circuit breaker to the outside of the box.

Next I wired the thick #8AWG wire between the fuse block and breaker, and the breaker and relay. I installed conduit fittings in the sides of the box that will later route all the branch circuit wiring through.

The cap to the master cylinder is still accessible, but its easy to disconnect the box from the mounting bracket if you need to move it out of the way.

Next I opened up the dash to get to the cigarette lighter to tap the power wire for my relay.

Here is a photo of the power wire of the cigaretter ligher that I spliced.

I unclipped the wiring harness in the back of the socket and then cut the red wire.  I used a regular wire nut and electrical tape to splice it.  I ran #14 wire back through the dash and into the engine compartment to the relay. (#1 wiring harness, #2 wire nut splice, #3 wire from relay)

I reset the circuit breaker, put the key in the iginition, and used a voltage meter to test the fuse block. Works great!  Here's a look at the engine compartment after the install:

UPDATE:
I realized the cigarette lighter on the passenger side marked "Battery" is constant power. The lighter on the driver's side is ignition only power. So, I had to switch my splice for the relay over to the driver's side.