Adding an Auxiliary Fuse Block to a Vehicle PDF Print option in slimbox / lytebox? (info) E-mail
Written by Mark Sound   
Monday, 10 January 2011 23:53

This will explain how to add an auxiliary fuse block to any vehicle. I have added this to several vehicles for various purposes and occasionally added multiples to one vehicle. The most common use for a fuse block is creating a convenient and safe place to add additional electric accessory to a vehicle. This will create a much neater installation than running individual wires to the battery.


I like using this style of fuse block because it only requires one power lead and uses standard fuses that can be purchased anywhere. Unless you are placing the block very close to the battery you will also need a high amp circuit breaker or fuse to protect the wire from the battery to the fuse block.

This is a good example of a circuit breaker and the type I like to use.

The first thing you should do is figure out what you are going to power with the fuse block. this will tell you 2 things how many terminals you need on the block and how big of a circuit breaker you will need. When selecting a circuit breaker add up all the devices amp draw and then add a little extra. I usually build these systems with extra for expansion later. In other words get a bigger circuit breaker than you need and get a block with more terminals than you need. How much is up to you.

Now you need to mount the breaker and block. Place the breaker as close to the battery as possible and the block near where you want the extra circuits.

Next you will need to select the correct wire to power the block. This will depend on the size of the beaker and the length of the run.

Use the chart above to determine the appropriate wire size for your application. When in doubt go bigger. This chart also includes a handy watts to amps conversion for auto applications. Note that this chart only applies to 12v auto electric systems.

Now run your wire. I usually start and the breaker and work out. Run the wire from the breaker to the battery. Use extreme care in the routing of this wire. Make sure that it in no way can touch any metal surface and think about how things will move when driving. This wire will not have any short protection and can be dangerous if routed improperly. Also think about what might happen should the wire break free from the breaker. If this is not possible try a new position for the breaker.

Next run the wire from the breaker to the block but keep the breaker off or disconnected from the battery. Always disconnect this from the battery first. Use caution when routing this wire so that it wont rub on any metal surface or pass too close to anything hot. if you need to pass through a metal surface such as the fire wall it is best to drill a new hole and use a grommet to protect the wire. Also secure the wire so that it can come lose and short out. I usually pull the wire and get the correct length plus a little bit before securing it then take it out and cover it with some type of covering for extra insulation. My preference is heat shrink tubing and expanding sleeving. Now put the wire back in and secure it to the vehicle. I usually shoot for every 6 to 8 inches.

Now you can plug in the accessories and add fuses to the block. Do not put fuses in the unused terminals and use the correct fuse for the accessories draw.

You can purchase the fuse block and breaker from some auto parts stores but I use most of the time.

Last Updated on Wednesday, 12 January 2011 02:26


#3 Ivan 2015-02-19 18:12

Thank's for posting the information. I'm using it to install an aux fuse block in my Bricklin for the likes of gps, cell phone charging etc.

#2 Mark Sound 2011-09-20 21:41
Quoting Canadianman:
This really is a very useful chart. Were did you get it from?

A google image search for "wire size chart".
#1 Canadianman 2011-09-20 19:28
This really is a very useful chart. Were did you get it from?