Question: Fuse EFI NO.2 (40) and Horn. (How work this fuse?) Help!!

[WD_T4R]

Hi!! Today I wired a small auxiliary Wolo Horn with a switch and a relay.
I added an Add-a-fuse to provide power to circuit 30 and 86 on my relay.

Basically, I want to turn the truck off, turn ON the horn switch and if somebody try to break in my 4Runner 2018 during the night, as soon as they put ignition, it will trigger the hidden horn. (I have other kill switch too don’t worry)

So I tapped into the 7.5amp fuse (40): EFI NO.2 because it seemed like an ignition hot slot after my tests.

Everything was good, the switch was ON, the truck was OFF and the horn was quiet. I turn the key to ignition to test it and the horn was blowing so all good.

4 hours later, it’s 10PM, i’m about to go sleeping and the horn start to blow randomly!!! (I want it to act this way but only when there is an ignition signal so something is wrong)

So my question: Is this fuse, sometimes, become an “always hot” circuit? I know it has something to do with the electronic fuel injection system so maybe something in the EFI systems start randomly sometimes? I don’t know very much about it.

I disconnected my horn and was hearing a little sound, i think it was the fuel pump or something in this area (near the fuel tank) so maybe something starts working and that’s why it has triggered my horn?

Thank you for your help

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[Aerodan]

Bump. The Magnuson supercharger taps the heat exchanger water pump into EFI no2. The water pump turns on and runs periodically for 10 seconds or sometimes longer. I had it run for seemingly a minute+ one time while I was wrenching on the vehicle.

Does anyone know why the EFI no 2 fuse gets periodically gets power when the vehicle is off?

 

[Bmnorm2]

Maybe it’s part of the Evap system circuit that occasionally runs to equalize pressure while vehicle is off?