Disconnecting 12 volt charging from vehicle

[Shadious]

Hi all- I’ve got lithium batteries and wanted to disconnect the 12 volt charging from the alternator. This is a 2014 21C and I found this just junction box up front under the bed. Is this where I would disconnect the charging wire, or would that be in the rear with the batteries? I did not find anything similar to what I’ve seen in other posts and wanted to take care of this while the panel over the bed is still removed.

 

[Centex]

You found the best place to do this.

Identify the charging wire on the umbilical cord from the vehicle and disconnect that from the trailer-side wire(s). If there's more than one trailer-side wire connected to the umbilical charging wire (likely the breakaway-brakes power feed from the battery), be sure to leave those connected to each other.

Carefully insulate the disconnected charging wire end so there's no risk of it contacting any wire or the metal box.

If you try this at the 'battery-end' of your system, you risk losing breakaway-brakes or other functions, don't go there, this is the place!

Have Fun!

 

[Shadious]

You found the best place to do this.

Identify the charging wire on the umbilical cord from the vehicle and disconnect that from the trailer-side wire(s). If there's more than one trailer-side wire connected to the umbilical charging wire (likely the breakaway-brakes power feed from the battery), be sure to leave those connected to each other.

Carefully insulate the disconnected charging wire end so there's no risk of it contacting any wire or the metal box.

If you try this at the 'battery-end' of your system, you risk losing breakaway-brakes or other functions, don't go there, this is the place!

Have Fun!

So looking at these connections, I’d say the large black wire is 12volt positive feeding the two smaller red wires. The larger of the two red wires is likely 12volt charging and the smaller the trailer breakaway?

 

[Centex]

So looking at these connections, I’d say the large black wire is 12volt positive feeding the two smaller red wires. The larger of the two red wires is likely 12volt charging and the smaller the trailer breakaway?

Personally, I'm very careful about wiring, don't like unanticipated surprises, I would not guess even using 'best apparent logic'.

It's too easy to use a multimeter to positively () identify the charging feed from the umbilical cord.

Disconnect the wire and look for continuity from the known charging pin on the plug using a long jumper-wire or look for 12V+ with the cord plugged into the running vehicle with no lights on.

 

[Shadious]

Sounds good- it’s raining now so I’ll have to pick this up at a later time..

 

[Thane-ESC]

Perhaps you could pull the fuse on the tow vehicle that protects the hot wire on the 7-pin wiring harness, that removes the power supplied to the trailer. That’s what I do when I am running a dedicated battery to battery charger to charge my trailer battery and don’t want two power sources applied to the trailer battery.

 

[Shadious]

Perhaps you could pull the fuse on the tow vehicle that protects the hot wire on the 7-pin wiring harness, that removes the power supplied to the trailer. That’s what I do when I am running a dedicated battery to battery charger to charge my trailer battery and don’t want two power sources applied to the trailer battery.

The problem with that option is that it takes the power from the breakaway switch. Definitely don’t want to lose that safety backup!

 

[Centex]

The problem with that option is that it takes the power from the breakaway switch.

That's not correct, the breakaway-brakes only come into play when the trailer is separated from the vehicle and must rely solely on the trailer battery for power in that terrible circumstance.

This is why you must not be plugged-in to the vehicle when conducting your regularly scheduled 'pull-the-pin breakaway-brake test'.

You can certainly cut the power to the vehicle charging pin by pulling the appropriate fuse in the vehicle, with the same result as disconnecting it in the junction box as far as the trailer is concerned.

I tow multiple trailers, some use the charging from the vehicle, some don't, so for me it just makes sense to mod the applicable trailer once rather than the vehicle each time depending on the trailer used. All trailers and the truck are always 'ready to hitch and go' in any combination.

YMMV.