Couldn’t find a dual-purpose fuse box so I created one

There are things that need constant 12v power and things that need switched power.  I figured it shouldn’t be hard to find a decent fuse box that has a relay and two banks of fuses. 

Well, I couldn’t find it.  So I made one out of a BlueSea fuse box. 

It has 12 fuse slots and is bussed which means that the power supply side of the fuses are all connected.  

So it needs just one connection of power. It also has a negative bus on the other end for grounds. 

https://www.amazon.com/Blue-Sea-Systems-Blade-Block/dp/B001P6FTHC/ref=asc_df_B001P6FTHC/?tag=hyprod-20&linkCode=df0&hvadid=312128389336&hvpos=1o1&hvnetw=g&hvrand=8884776562989181242&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9031008&hvtargid=pla-383472770805&psc=1

I took it apart and cut the bus in half so only the bottom half of fuses are connected to the constant 12v lug. 

I removed the negative bus and bolted it under the dash to use as a negative bus, only not attached to the fuse box  

I bought a heavy duty 50-amp relay and mount that I put where the neg bus was. 

I ran power from the hot bus to the relay and then back to the other bus.  I ran the relay trigger wires out of the box that will go to ground and to a key on trigger wire. 

Thanks for detailing that.  My last wiring project I was dismayed by the same thing, but I ended up with bus bars feeding a fuse box.  This is a lot cleaner!

I am a little confused at what exactly is going on, so I will have to buy one of these to tinker with.

Nicely done!

Another way that could be done is to separate the + bus and feed it switched power from the side through a large fuse.

There used to be a company that made a custom fuse panel. I can't find it now or remember the name of the company for the life of me.

It had three terminals for every fuse, arranged in a row like this:  - - -

The center was the output from the fuse and one side was switched power, the other was constant.

Example: Put the fuse on the left side and that circuit is now controlled by keyed +12, put the fuse on the right side and that circuit is now +12 from the battery.

It was in a customer's car that I haven't seen in years but I thought it was a great idea.

Knurled. said:

I am a little confused at what exactly is going on, so I will have to buy one of these to tinker with.

He cracked it opened and split the main bar here:

He then hooked the the bottom of half of the bus (right half in the picture above), so the switched power to it is driven by a relay:

Which he triggers with these two wires:

Note that he modded in the relay block (bottom of this image), by removing the grounding bus bar that's present in the first product picture (top right in that picture).   He did have to cut the pretty clear cover in to fit it (his last picture).

In reply to bentwrench :

You could, but everything on that bus would be limited to the circuit you pulled from. If you have a spare accessory outlet and ran it through a fuse to that side of the bus, you are limited by the wire size. 

This way I ran a large wire (8 ga I believe) from the battery and it is controlled/switched on by the relay which pulls a very small amount of power that I just grabbed from the radio power (which was no longer hooked up to the radio because I am pulling it off of my new fuse block). 

I could have just run the former radio power wire to the switched bus but it was a 7amp fuse and I’d like to be able to run things like the stereo, seat heaters (as a gift for my wife),  maybe phone chargers, an amp perhaps, etc and this way I’m not limited.

i am running a 50amp circuit breaker at the head of the run, right off of the battery, in case there is a short between the battery and the fuse block. 

In reply to ShawnG :

That’s a great idea!   The only issue I see is putting a removed fuse in the wrong way   But very clever  

Oh, okay!  I didn't see where he split the bar.  Was thinking longitudinally, which made no sense.

I like it.

You know, thousands of European cars used these fuse boxes with some success... sometimes

CJ said:

You know, thousands of European cars used these fuse boxes with some success... sometimes

... And in a pinch you can use a .22?

In reply to WonkoTheSane :

Yup.

Those Blue Sea Fuse boxes are great. I replaced most of the factory wiring in our Chumpcar that was split between two fuse boxes to one of those and have another one for accessories like the fans, light bar, running lights, etc. 

Great job making this fuse box do what you need. I looked hard at these before settling on a Cooper Bussmann 15303-2 on my Fiat project. The Cooper was more compact, and offers bussed and un-bussed configurations, so you have flexibility to do what you need. I think in your application, you made the right choice.

I really like that bussman.  I looked at it and can’t remember why I decided against it but I think it would have worked quite well. Actually I think it’s because I needed less relays under the dash and more fuses.  

 Regardless, I think it looks better than the one I got but this is under the dash so I’m ok.  And I’ll use the same under the hood for continuity and the same fuses and relays.