You know how the +12v lighter outlet goes low (0 volts) when the vehicle is off? I'm looking for any line under the hood on the drivers side of my 2013 Trail that does the same. I don't need to pull much power from it just enough for the gate signal of a MOSFET to control a dual battery solenoid.


Before anyone tries to tell me better, let me explain, the MOSFET will get its solenoid drive current from the battery - NOT the +12v on/off line. I am simply using the +12v on/off line to synchronize the charging of an AUX battery with the running of the vehicle.


The problem is my AUX battery is a Lithium Iron battery which has an resting voltage of 13.5+. This will fool any micro controller based solenoid supervisory circuit in to thinking the vehicle is still on. To defeat this I am simply planning to run the solenoid off any vehicle on/off signal I can find under the hood.

Or perhaps someone may know of a more elegant way to handle an AUX battery of higher resting voltage?

Thanks in advance,
Joe

I think I understand what you're trying to achieve, and I can't readily offer any suggestions for a tap source under the hood without going to look (which I will this afternoon).

But, can I ask a separate question: why are you running a LFP battery as your auxiliary?

Because it seemed like a good idea at the time and now I am somewhat committed... Hind sight, I would not have done it this way because I really don't need the capacity and it presents more complications and problems than it is worth.

At the time when I decided to do it I was in the process of converting an underwater vehicle over to LiFe batteries. I was so impressed with the difference in capacity (in my excitement) I went ahead and bought an array for the 4R.

Now I'm financially committed. Unless of course anyone is looking to buy a like new and almost completely unused 60Ah LiFe battery... $400

Maybe you can try contacting @Titanpat57 to see where he tapped into? I think he did a similar dual battery install to what you are thinking about doing: Dual Batteries on the Cheap

Pat never did find a source under the hood. I checked and couldn't find one either.

Just get a fuse tap for the "P-OUTLET" circuit in the drivers footwell and run the wire through the factory grommet under the hood.

Gotcha. If @Titanpat57 couldn't find a source under the hood, I would recommend what @Antman did. Pulling one wire through the firewall is pretty trivial and will likely be the less complicated solution. Occam's Razor!

Now you reference the P-OUTLET as being in the footwell. Is this the entry point for the wire that carries power to the center console power outlet or is it something else? You wouldn't happen to have a picture of what you're talking about would you?

Thanks in advance Antman you rock!

It's in the fusebox. Here's a pic of the fusebox cover and a fuse tap you can use to access the circuit without cutting/splicing.