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[N4SRN]

I'll look for that stud bolt mentioned. I found some fuse connectors but they are 16g 15AMP. OK if no stud bolt?

[W8JX]

Mark, we do not agree on much but do here. Today's "smart cars" that can even report a burned out light bulb require a different mind set for powering add on accessories than from the distant past when a direct battery connection was the path. You need to feed your rig from main fuse panel and not battery and anyone that suggests that a direct battery connection is better has no real understanding how modern cars work. Kinda like the IT guys that always recommended nuking and re-installing windows as SOP to fix a problem because they were pretty clueless too on how and why it works and how to fix it proper.     

So how does one connect through the fuse box? Is there a fuse with a power connection that I can just plug in?

Typicality a car/SUV will have a few fuse panels. A main one usually under the hood and at least one or more in car somewhere. Locations vary with car/SUV.  Main panel, usually under hood, you will find at least one unused aux feed with no fuse in it and a stud to bolt feed too. (it is that way on GM trucks/SUV's and main panel is protected with a fusible link from main battery) On sub panels in cars they is usually empty sockets as well that have spade connectors on them. Also remember that fuses in sub panels are all fed from same buss or buses meaning that they are all capable of same current potential within limitation of main buss fuse under hood.

I think he meant what does he use to actually make the connection.

On main fuse panel aux terminal is typically a thread stud with a bolt and you can use a terminal lug of correct size. On sub panels you typically use a female spade connector.

[W8JX]

I'll look for that stud bolt mentioned. I found some fuse connectors but they are 16g 15AMP. OK if no stud bolt?

This can work. Some would be amazed at the amount of power/current that goes though car circuits (wiring and fuse panels) on wiring sized smaller than they think is needed and thru spade connectors and it does it day after day, week after week, month after month, year after year without failure, melted wiring or fires. When you look are wire current ratings, when run in romex in a house vs in single wire like in a car, the safe current capacity of wire is a lot higher in single wire runs. 

[N4SRN]

Here's my main fuse box under the hood. No stud bolt I can find, unfortunately.

How does this fuse tap look? Is 10Amp enough?  https://www.amazon.com/gp/aw/d/B001QRSBW0/ref=mp_s_a_1_8?ie=UTF8&qid=1488117531&sr=8-8&pi=AC_SX236_SY340_QL65&keywords=auto+fuse+tap

[W8JX]

The minimum buss feed for those fuses is 30 amp after looking at picture. The fuse feed in question will have no trouble powering rig. Also remember a 30 amp fuse does not blow at 30 amps. That is is designed load. It will blow 15 to 25% above that and are slow blow in nature.

[K1WMT]

It would have saved me a lot of thinking if I had found and read this thread before I began tricking out my Subaru and my garden tractor.   

I concluded as others advised, there was really no need to connect directly to the battery and to instead use the fuse block.  Even today, most home installation gear advises going directly to the battery: entertainment systems, lights, etc. etc.  I think the reason is to prevent the really clueless DIY'er from screwing up the wiring/breaking something that is buried deep in the chassis. 

At the battery, at least the problem is quite isolated.  A downside I see is to direct battery connection is not being able to connect to the switched side of power distribution, which can drain your battery if left on.  Another think I always ascribed to is keeping all your grounding connections in one spot to avoid any chance of a ground loop.   Just like we do on the RF side.

Someone asked how to connect to the fuse block.  There's a really easy way nowadays, with a pre-made fuse holder pigtail.  Sometimes called "add-a-circuit", they are easy to find (ebay) and as cheap to buy as to make.  Also easy to remove if its ever necessary.  Just make sure you plug it in the correct direction, so you are on the fused side, not the unfused side.  I'd post a photo but I don't see an icon to let me do that.

For my lawn tractor, I went as far as buying a small fuse block, as I keep adding electrical stuff to it. 

[W7CXC]

Opinion..... to the place right below the "BU" in the photobucket picture. with an inline fuse coming off that post.

[KM3F]

From 2015 on, your Subaru has >>battery management system<<.
The positive cable at the battery you see in your photo, has the Sensor to feed info back to a control module.  Note the Sensor has a cable plugged into it for the monitoring the battery state of charge and control and feedback.
This control system varies the charge current according to certain conditions that vary.
The battery is usually an AGM type that has different operating requirements for such things as temperature, tracking of it's life and usage and charge control under varying conditions.
Any add on circuits need to reference chassis ground >> not at the battery terminals<<
and >after< the Sensor in order for the Sensor to include the drains in the overall system operation.
Vehicles with Auto Stop/Start are critical to this operation or that can function fail.
Some management systems in other makes have the Sensor in the Negative lead but operate the same way.
Vehicles are no longer old school with just an Alternator/Regulator with a Flooded Lead Acid battery.

[WA8NVW]

So why am I seeing people with 2x1 and 1x2 extra class callsigns who don't know how to connect a simple 12VDC relay in the positive lead that runs into the cabin to feed the radio equipment?  Public safety has been doing this stuff for decades, guys.  If you don't know how, hire a pro from either your local 2-way radio dealer or autosound shop.

[KM3F]

Well, all I can tell you is the Extra class now means technically very little but added band privleges and an agreement to abide by the rules.
Studying the questions and really wanting to undersrnd the correct answer is secondary to the point, very little is really learned in the end.
It's about like looking at an Ipad or Smart phone all the time. Very little is actually learned or retained very long since it's always there to see again, and still not leaned to any extent.
Take it away and user gets sorta lost lost in a hurry without it.
I don't own one and doubt ever will.
For my next trick in a group presentation, I will ask if anyone knows how Battery Resistance is figured. They will be surprised how simple it is not ever having to really know, on an ongoing basis and why it's in play in vehicle.