I'm in the process of adding an instrument (will writeup later) to my 4runner. I'm running power from the fuse compartment in the engine bay and I realized that I messed up.

Since I ran it directly from the source I just made a circuit that will have power whether the vehicle is off or on. This is not good, I don't want the LEDs on when the vehicle is off.

How do circuits like the radio turn off automatically when you turn the key to the off position?

Some circuits are triggered by the key in the "ACC" position (radio), others in the "ON" position, others only in the "START" position. The key cylinder has 'outputs' for each of those positions, which then triggers a number of relays, to power each of the circuits that need to be on at those times.

Get the diagrams for your truck and figure it out...

-Charlie

So it's possible that there is a common bus bar for ACC controlled circuits within the same fuse box and all I would have to do is connect my circuit to it?

I'll check my service manual

Checked the body electrical section, not very helpful. It doesn't go into how the ignition controlled circuits get power and work. The closest thing is on BE-13 that shows a diagram of the ignition switch and the continuity of each pin at the different positions.

Also what does the integration relay circuit do?

Yes... map the box with a voltmeter, see what has power when key off, then key on and check to see what didn't, that now does ~ those are the circuits you want. The lid will tell you which are which so it's pretty easy to Id anyway.

IIRC, there are several together... the center of the 3 main rows? Been awhile... FWIW, if you're running a heavy load, i'd be smart to use a relay.

Just checked every bus bar in my fusebox. As I feared there is no one relay that powers an accessory bus bar.

All busbars are connected to the battery at all times, if you want to have circuits that aren't always on, you have to splice into the ignition system to power a relay when the key is at the acc or on position.

Its impossible not to splice or tap into the stock wiring harness unless your fine with manually killing the circuit every time you turn the car off or.

It might be a different story with the interior fuse box but I doubt it.

I'm not running a heavy load at all, I think the spec sheet said under an amp. But I hate the idea of adding janky fuse taps or splicing into the existing wiring harness

Most of the switched power wires will be inside the cabin...

White-Blue (white with blue stripe) will be around the engine bay and power a bunch of VSVs, etc. that you can at least use as an ignition trigger. It doesn't go to the main fuse box in the engine bay, as far as I can tell, but it should run in that bundle and be found at most of the 12V sensors and VSVs in the engine bay.

-Charlie

I fuse tapped an interior fuse that was already ignition controlled. I didn't want to, but there is no way to accomplish what I wanted without splicing or fuse tapping. Since fuse taps are easier, and this device wont be too powerful, I'm went with fuse taps. The draw for powering a relay vs a the device itself wouldn't be all that different.

Hopefully Toyota put sufficient safety margin to handle a small increase in load. I'll measure it with a vtvm and see what the draw is.

The number of fuse-taps I've used over the years.... probably have half a million miles with them installed. All were just relay triggers, and I put 2.5a fuses on them so they would blow easily (none did that I remember). There's plenty of overhead for a relay (about 1/3rd of an amp).