Installing Dash Accessory Fuse Block Powered by Coach Battery

 

I generally draw power from the battery disconnect relay post, but this is inconvenient because it necessitates removing the driver seat every time I need to power something. Installing a fuse block powered by coach batteries under the dash is the simplest approach to future-proof any aftermarket additions.

Finding a suitable placement for the fuse block is not as simple as you might assume; there is barely enough space beneath the dash to put a good-sized fuse block. You could place one over the dash plastic trims, but that would look unprofessional.

There is a small space behind the steering wheel lower trim for a small 6-way ATO fuse block; it will be hidden but easily accessible. 

Supplies you'll need:

• 6-Way ATO Fuse Block Kit
• 10-ft 8-AWG wires
• 8 AWG-#10 Stud Tinned Copper Wire Lugs
• 40-amp Stud Type Auto Reset Circuit Breakers If you need a higher capacity breaker, you need to upgrade to a bigger gauge wire. The fuse box is rated to 100-amps.
• 3/8-inch PET Expandable Braided Cable Sleeve (optional)
• 1/2-inch heat Shrink
• Zip ties

Tools you'll need:

• Pliers, Wire stripper/ crimper/ cutter
• Hydraulic Terminal Lug Crimping Tool  I have this tool for years and made crimping heavy gauge terminal lugs a breeze, but any crimping tool should work.
• Socket wrench for removing and installing ground bolt/ battery disconnect terminal connection
• Torx bit t-20 driver
• Heat gun

Step by step procedures:

Before starting, disconnect the chassis battery and coach battery (not pictured) ground wires. Always wait at least 10-minutes after engine shutdown before disconnecting the chassis ground to allow Sprinter emission control system to complete cycle.

Remove steering wheel lower trim cover (secured with 3 T-20 Torx screws).

Remove driver-side rubber floor mat

Remove center console base floor trim and battery floor cover.

At this point, you have to remove the driver seat to access the coach battery disconnect. Make sure to unplug the chassis ground disconnect before unplugging the seat belt sensor wire or you'll get a dash SRS warning light error. 

The driver seat is only held by 4-bolts. The seat is heavy and will remain tethered into the seat belt so you cannot move it far from the base.

Wire routing of the positive cable from the battery disconnect relay post. You can also opt to wire the fuse block direct from the battery under the hood, but I'll be upgrading to Lithium's in the future. The Lithium batteries will be installed behind the driver seat.

The 40-amp auto reset breaker is mounted next to the battery disconnect relay as shown. It is connected to the battery (+) terminal post, this post is always powered by the batteries.

The 8-AWG wire run to the fuse block

The fuse block ground wire is connected to a ground post at the base of the center console (passenger side).

Positive and ground wire routing to the fuse block.

Wide shot of the fuse block location.

Another shot angle of the fuse block

For now, the dash DC outlets (on this post) and the Android head unit (on this post) are wired into the fuse block.

The fuse block with cover and labeled. Replace the steering wheel lower trim covers, reinstall the driver seat, reconnect the seat belt sensor wire, then reconnect the chassis and coach battery ground wires and you're done!