Should I Install a Relay To Cut Power To Trailer Battery Charge on 7-Way with Vehicle Off

Updated 03/21/2022 | Published 03/19/2022

Question:

I am nearly done installing a universal 7-pin wiring system on my 2010 Toyota Highlander. It has occurred to me that the way this is set up, the high amperage lead from the battery to the trailer is not switched in any way. It seems to me, that this could cause issues with killing the cars battery if items are being used in the trailer while connected to the car and the trailers battery is not fully charged. Would you recommend a relay on this circuit that is tied to the cars ignition for on/off control?

asked by: Homer S

Expert Reply:

The battery charge line circuit is not keyed in many vehicles from the factory meaning it has constant power. If you wish to install a simple isolator then you can do so but a better option is the Redarc Smart Start Battery Isolator with Wiring Kit part # 331-SBI12KIT which actually monitors the status of the start battery and uses that to determine when it should charge the aux battery. It can also pull power from the aux battery to charge the start if something goes wrong. This is a must have if you boondock as a dead battery could spell disaster.

expert reply by: Conner L