Running Engine Detect?? For duel battery

Any help appreciated. I'm looking for a way to have a 12VDC power source only when the engine is running. Not when the ignition or accessory is on.

My past use for this has been to energize a relay connecting my two batteries together. On my other vehicle the fuel pump shuts off upon low oil pressure, stalled engine, etc.. So, I utilized the fuel pump power to activate the relay. Also have a push button switch in the cab to connect the auxiliary battery if the main is too dead to start the vehicle.

I'm looking to do very much the same for the Tacoma. I'm thinking possibly something out of the Engine ECU. A low power signal may require an additional relay to power the constant duty battery relay/solenoid/contactor, etc..

 

Use a smart isolator. Way easier. That’s what I did for my DIY dual battery. The isolator knows when the vehicle is running

 

The "Smart Isolators" I've looked into only compare battery voltages and then disconnect. How does yours wire in? I would like to take the "Smart" out of everything and keep it simple and trouble shootable as possible.

 

That’s how mine works. When the battery voltage gets to a certain point is connects the batteries. When a load is on one it disconnects, and it has a manual disconnect switch.

 

How do you open your fuse box?

edit: OP, I don’t have the EWD for the 3rd gen but on my 2007 (assuming you also have the bed power outlet), the factory wiring will only let you use it with engine running. So there’s a relatively easily accessible circuit for you.

 

Thanks, I will look into that. I have some familiarity with the circuit as I have removed my bed outlet and put one in the cab console AND done the 400W all the time mod. I will have to review the Anytime 400W threads.

 

Have to remove one or two wires from the positive terminal. Not a big deal since I carry tools

 

Just got back into this project. Unfortunately, that circuit is a data signal from the Engine ECU to the Inverter. Some pulse width sort of signal to the Inverter.