Wiring Second Trailer Battery with Dual Battery Controller and Isolation Solenoid

Question:

Hello, I have the ETBC7 kit installed on my 2011 FJ Cruiser along with a Curtis brake controller. I also have a home built trailer with electric brakes. All of that has been wired and is functional. I want to add a 3rd battery to my electrical system for the trailer. I am trying to find out how to go about wiring this. I have a National Luna dual battery controller. The manual for the controller says I should run a positive and negative wire to the trailer battery along with a circuit breaker from the 2nd battery. Do I really need to do this or by using the 7 pin connection kit is everything in place. Currently the power wire to the 7 pin is on my main battery. Before I move it I want to make sure no other changes are required. I am guessing if the system is ready to handle the third battery with no additional wiring it would simple mean I need to move the positive and negative wires which were installed on my primary battery over to my 2nd battery. The only other thing I can see adding is a solenoid to prevent battery drain when my FJ is not running. Thanks for any guidance. All of the kits from eTrailer have been great. It has made it a simple process to wire my trailer and convert the FJ from a 4 pin to 7 pin.

asked by: Chris K

Helpful Expert Reply:

The 12V charging circuit on your FJ Cruiser's 7-way should already have a 40-amp circuit breaker in place to protect the vehicle battery and wiring from excessive current draw from a shorted trailer wire, for example, or from too-high power demand from the trailer. This will be sufficient for single trailer battery applications but if adding a second battery - a second item that wants to pull power through your 7-way and through your other battery - you should follow the instructions from your controller and use the specified secondary circuit breaker. This is there to protect your first trailer battery.

You are correct that you will want to install an ignition-controlled isolation solenoid, part # PK5231201, to stop current flow from your FJ's battery when the ignition is off. This is especially important with two trailer batteries trying to pull from it. You'll need a fuse tap kit # F2526 to access a key-controlled circuit such as that for a power antenna.

expert reply by: Adam R