Question - Looking for 12v signal that engine is running

I have been through several searches but haven't found what I am looking for.

What wire can I tap into that is only energized when the engine is running. My truck is 2nd gen Tacoma, 2013 DCSB Sport base model.

Basically, I will use this signal to energize a relay so something can only turn on when the engine is running.

Any help is appreciated.
Sam

 

Does it have to be only when the engine is actually running? or when the key is in the "run" position? Because you could easily use a fuse tap on a circuit that is only live in that position(like reverse lights), but it wouldn't detect if the engine is actually running.

Maybe something that detects battery voltage, and only triggers on when voltage is >12.8 or 13v could work for your purpose, activating when the engine is running and turning the alternator.

Unless you have the capability to engineer something like an arduino/rasPi that can read the OBD port. As TnShooter said, I don't recommend destructively tapping into any critical circuits like sensors or fuel pump. Kinda sending a golden invite to gremlins. I like making all of my wiring mods as easy as possible to return to 100% stock for this reason, even if it means ordering connectors and making jumpers that I can later remove if I wish.

 

Fuel pump relay or C/OPN relay would be easiest but if you don't want to disturb those, you can add a second N/O oil pressure switch dedicated to your needs.

May help to know what exactly it is you're trying to accomplish.

 

I like the idea of a voltage switch if the engine has to be running, but hopefully you can get by with key in the on position cause that's so very very much easier. Maybe you could use the power steering fluid pressure switch as a indication the engine is running, maybe you could buy a second pressure switch you could install at some hose junction so your not messing with the existing sensor, it would need to be a signal to a relay though.

 

Keyed hotwire underhood

 

Huh?

 

OP is confused on wording, and you are helping it go down hill...

 

I deleted all my post.
That way there's no confusion.

Looks like you got it figured out.

 

Key on, engine not running is "not" what I am looking/hoping for.
Application - installed a compressor and tank powered from main battery that automatically maintains 90-120 psi. However, I don't want the compressor to run if the engine is not running as it pulls a lot of power. There may have been an occasion or 2 where I neglected to turn off a manual switch and don't want to end up with a dead battery.

I also want to keep it simple, adding pressure switches, etc. is not really what I want either. Perhaps just key on would be fine.

 

Well imagine that........
I wasn't confused after all....


Not directed at you OP.
But I won't be "helping" in this thread.
I'll Caribe Makaira help you.

Best of luck to you man.

 

Buy something like this that cuts off power once the battery hits the selected voltage, this would of course just be the relay input trigger.
Looks like its discontinued so you can buy used or something similar.
https://www.amazon.com/BlackVue-Vehicle-Battery-Discharge-Prevention/dp/B008B8ERIO