Dual Battery Installation - Toyota FJ Cruiser Community

- Dual Battery Installation By: sbechtold on fjcruiserforums.com
Preface:
I recently completed a dual battery and fuse block installation install in my FJ and thought I would share what I did in
the hopes that it is useful. I also moved all of my aftermarket electronics over to the new fuse block, which was like
reinstalling everything (read: PITA). Hopefully, this will be helpful to someone and if you find things that make it even
better please add them to this thread so future installations benefit from the knowledge share. While a Dual Battery installation by itself is not that difficult, I found that rewiring all of my accessories was time consuming. This was a BIG
project that took A LOT of effort and time. Be prepared to spend some good quality time with your FJ and be prepared
to get to know it intimately. If you choose to undertake installing a dual battery system and have questions feel free to
PM me. If I can help I will. Happy reading!
All of the images in this thread are “clickable”, so feel free to click on and image to view a larger picture.
Reason:
I decide to install dual batteries and a new fuse block in my FJ for a few reasons.
1.) I wanted to run all of my electrical accessories (offroad lights, rock lights, backup lights, CB, inverter, fridge, electric blanket, etc.) from a second battery.
2.) I wanted to isolate the starting battery to prevent a dead starting battery situation (don’t like getting stuck in the
middle of no-where).
3.) I don’t like having my winch powered by my starting battery (goes back to that whole dead battery thing).
4.) I don’t like having miscellaneous fuses and wiring all over under my hood and dash, hence the fuse block.
Parts Needed:
1 - Painless Wiring Dual Battery kit (available at SummitRacing.com)
1 - Blue Torch Fab battery box (available at Blue Torch FabWorks)
1 - Optima Yellow Top battery (34/78 series battery purchased at local auto parts store)
1 - Blue Sea 12 Circuit Marine fuse block (purchased from West Marine)
15’- #2 Battery cable (purchased at local welding shop)
4 - #2 Battery cable lugs (purchased at local welding shop)
3’ - 1.5”x1/5”x1/8” angled steel (purchased at Home Depot)
3’ - 1.5”x1/8” flat steel (purchased at Home Depot)
5’ - #6 red battery cable
1’ - #6 black battery cable
4 - #6 battery cable lugs
6 - Stainless steel bolts, washers and lock washers (purchased at Home Depot)
1 - 15” #2 battery ground cable (local auto parts store)
1 - positive battery terminal (marine style with post & wing-nut)
10 - 12v LED’s in RED and GREEN (delcity.net)
Miscellaneous items - Shrinking tubing, wire, zip-ties, electrical tape, 1/2” rubber grommets (and other stuff that I’m
probably forgetting... )
The Install:
Battery Tray & Battery Box - Installation
Once I figured out that I wanted the battery installed as close to the firewall as possible I started to fab a battery tray
for the BTF battery box to set on. Here are a few pictures of it in progress and finished. This is the tray about half way
finished. I added a few legs going toward the front of the engine compartment to stabilize the battery box. In the end, I
chose to welded the battery box to the tray I made, then bolted everything to the fender. I mounted the battery tray and
box to the fender with stainless hardware. I sprayed rubberized undercoat on the bolt heads once I was finished.
Installing the Solenoid
I installed the solenoid on the drivers fender. I moved a small electronic unit that sits directly on top of the wheel well
in front of the master cylinder. I removed the bracket and bent it slightly until it lined up straight with one of the other
OEM bolt holes in the fender. I then used the bolt hole where the electronic unit was located to hold one end of the solenoid. I drilled a new hole in the fender to support the other end of the solenoid. I installed the bolts and was done with
the solenoid.
Wiring - Batteries, Solenoid and Winch Power
I created a new 2/0 gauge positive battery cable that is about 15” and had lugs on both ends. This cable goes from one
of the terminals on the solenoid to the positive terminal on the battery. I then created another long (approx. 10’) cable
(the RED one in the pictures) that runs from the other terminal on the solenoid to the positive terminal on the AUX
battery. I chose to run the cable behind the fuse box and battery, then across the front of the engine compartment. The
cable is zip-tied to the OEM wire loom that runs under the front sheet metal just in front of the radiator. It’s kind of a
pain to get zip ties on the cable, but it’s worth the clean look.
In order to get power to the new fuse block, I created another cable out of #6 wire. I ran the cable from the AUX battery through the firewall and into the cab where the fuse block is located. I installed the fuse block in the passenger’s
kick panel. I also purchased a 15” #2 ground cable and ran it from the AUX battery to a bolt located on the passenger’s
fender. There is a bolt located in the same location at the ground on the driver side fender. I used this same location as
the ground for the AUX battery. I then created a short 15” #2 cable and ran it from the AUX battery to my winch control box. The power line from the AUX battery to the fuse block has an 80amp in-line fuse to protect the electronics that
will hang off the fuse block.
Wiring - Fuse Block
I ran the #6 wire from the positive terminal on the AUX battery through the firewall into the cab. The cable is connected to the fuse block that is mounted behind the passenger’s kick panel. During this installation I moved all of my
accessories over to the new fuse block (what a PITA!). I mounted the Blue Sea Marine 12 circuit fuse block with zip
ties. It is mounted to the existing plastic wiring mount and the surrounding electrical wiring. The fuse block is very
stable and the passenger’s kick panel fits back on with plenty of clearance. The power line come in through the firewall
from the AUX battery. There is a factory grounding point directly behind the fuse block that works well for grounding
the fuse block. All new electrical accessories will be powered by the new fuse block. The first one will be my CB radio
that I will install in a few weeks.
Wiring - Switches
I decided to use the driver’s glove box as a location for all of my switching. I have not used my glove box for anything
and I never plan on purchasing the over-priced Toyota NAV unit. I used some 16 gauge sheet metal to make a switch
panel that mounts inside the glove box. I made some labels with a vinyl label maker, but I haven’t installed them yet.
I have also considered having Tap Plastics build me a switch panel with the name of each accessory engraved into the
plastic, but for now this will work. I had pre-purchased all the switches required for my planned mods from delcity.net.
I drilled a bunch of 19/32” holes in the panel and mounted it in the glove box with all the switches pre-mounted. The
wires from each component are fed up through three holes in the back of the glove box. I made sure to leave enough
wire so that I can remove the glove box if required. I created a wiring harness that feeds all the switched electrical accessories up into the back of the glove box and connects to each individual switch. There is also another harness that
routes the positive feed from each switch to one of the LED’s mounted in the front dash. Even thought the switches are
out of sight, the LED’s let me know when is actually powered up. While I was adding switches I decided to add one for
the A-TRAC Hack and the DRL Hack, so now “A-TRAC+Locker” or “DRL Off” are only a flip of a switch away.
Wiring - LED’s
Since the switches are out of sight I elected to install LED’s on the dash so I would know which accessories are on/off.
These are normal automotive LED’s that install into a 5/16” hole. I created one large loomed wiring harness that run
from the back of the glove box to the install location on the dash. Each switch that powers an accessory also supplies
power to an LED on the dash.
Wiring - Connecting the switch to the Solenoid
There are two wires that run from the switch to the solenoid. The switch is mounted in the driver’s glove box. The
Painless kit comes with a 3/4” rubber grommet that gets installed into the firewall. You need a 3/4” drill in order to drill
the hole and insert the grommet. Then pull the wires through and connect them to the solenoid. I had to move the small
silver finned electronic device that is to the left of the solenoid. I also had to bend the bracket so it would sit where you
see it in the picture. The solenoid is mounted using one (1) factory nut and a hole that I drilled.
System Operation / Testing
The toggle switch that comes with the Painless kit has three (3) positions. In position one the GREEN LED is illuminated and the system is operating in normal mode with both batteries available for charging, but are isolated from one
another. In position two the RED LED is illuminated and the system is operating in emergency mode with both batteries combined for starting and charging. In position 3 the system is off and only the factory battery is available for starting and charging. All testing went fine and the system is now working as described by the manufacturer.
Installation Comments
The Dual Battery Installation by itself is not that difficult and was not that time consuming. The Painless Wiring kits
was well put together and had great instructions. This should have been my first electrical modification as it would have
saved a lot of re-work on the already installed electrical accessories. I had to move all of the electrical accessories (IPF
lights, Backup Lights, IPF Fog Lights, Rock Lights, switching, CB and other stuff) from the factory battery over to the
fuse block that I installed as part of this project. I still need to move the 400 watt inverter over to the fuse block and
AUX battery, but that’s going to have to wait as I tired of doing electrical work...
There is a lot of good information in this thread starting around post #70 there are a few others that have started/completed their dual battery installations.