Add-a-fuse (fuse tap) and circuit questions - Does orientation matter? Circuit explanations?

I recently installed raptor lights (4Runner lifestyle kit) on my 22 TRDP.

When I first installed them, I just directly followed 4RL's tutorial video. When it came to installing the fuse tap, I popped it into the 10A "Tail" slot, with the fuse block pointing toward the front. This worked, and the tail circuit is nice, as the raptor lights seem to follow other exterior lights.

After doing some research online, I learned there's a correct way to orient a fuse tap - with the left side of the tap being powered by 12V. After checking with a multimeter, I found that the way the video instructed put the tap in backwards. The "Tail" circuit is in the corner and there's no room to have the tap flipped, so I moved it to the "KDSS" fuse (KDSS isn't present in the TRDP, but the fuse is there). Ideally, I'd like to be able to move the fuse tap back to the Tail circuit, or to a headlamp circuit, if one is present here.

I looked at the back of a Littelfuse tap box, and the instructions state (paraphrasing) "plug it in. If the accessory doesn't work, flip the direction" - which implies it's not a big deal. My understanding is that if it's reversed and the main (lower) circuit spikes, both circuits will lose power. If the secondary (upper) circuit spikes, only the secondary circuit will lose power.

With all this said, does the orientation really matter for low power accessories?

I plan to add a couple of other things that will require 3 additional fuse taps (2 circuits for compressor button + 1 circuit for dashcam), and I'm stumped on which circuits I'll use.

Is there a guide online that explains each circuit? Which circuits are always-on, which work only when the vehicle is on, etc?

I've seen guides for prior models, but my 22 model seems to have different circuits (see attached photo).

 

I doubt it really matters but maybe there is someone who can make a finer distinction.

Though I do have 3 fusetaps installed and never gave much thought to orientation. It's been years with no issues.

Just depends on how you want them powered.

Do you want them only powered when the key is in ACC mode or engine running?

Or do you want to be able to power them even if the engine off - battery powered.

I would choose ACC accessory power as you don't have to worry about forgetting about leaving things on and potentially draining your battery. But also depends what you are trying to accomplish.

 

Thanks, that's reassuring!

I think I'll move the raptor lights back to the "Tail" fuse - as mentioned, I like that the lights go on/off with the rest of the head/taillights.

For the compressor button, there are two circuits:

1. Button lighting - ideally, ACC mode. Is there a circuit that gets controlled with the rest of the dash lighting? (I.e., only turns on at night/when headlights are activated)
2. Relay activation - this should only come on when the engine is running

I think my dashcam may have a mode where it can record when the card is off, so I may want this to be plugged into an always-on circuit (I think the hardwiring kit comes with a circuit that monitors input voltage and stops draining the battery when it crosses a low threshold)

Which would be good candidates for these?

 

The fuse tap orientation does matter. If you orient it the wrong way you will be drawing current from the “output” of the OEM fuse (and it’s load) and not directly from the battery +12V. Your additional load current (to the raptor lights etc) will be going through both fuses instead of one. In the case of an overload of your lights the lower value fuse will generally blow first, but not always. The OEM fuse may be overloaded and blow more often. It’s not really a good practice to do this.
See the diagram below.

 

Bumping this thread w/ another question - does anyone know the difference between the three IGN fuses?

I assume "IGN" means these are all ignition-controlled? Wrapped up my compressor installation yesterday, but put the isolation/relay lead on an ACC-controlled circuit (for some reason, "KDSS" is ACC controlled), and I don't want to risk the compressor being enabled without the engine

Of course I'm fine testing the circuits to confirm they're ignition-controlled, but I want to make sure I'm not tapping into any mission critical circuits

 

Following this closely. I’m in the process of installing a SwitchPros 9100 in my 2020 ORP. I need to use an add-a-fuse to the “tail” and “acc” fuses, and have the same issue. The “acc” fuse is fine but there’s no room to properly orient the add-a-fuse in the “tail” slot.

Of all the install videos I’ve watched, none of the installers seem to test the fuse slot before putting in the add-a-fuse.

 

I haven't tried TAIL or ACC yet, but I found engine bay IGN slot tripped my ecu and lit up dash warning lights when I added piggy fuse holder (perhaps I was plugged in reverse polarity that time? I just learned from electroboy above).
YouTube dash switch video recommends interior fuse box open slot between #13/14. But I tested no voltage there. I actually successfully tapped multiple 12v loads into open slot above #4, which has acted the same as IGN for me!

Edit: I see now from OP newer fuse box covers show my fuse slot actually labelled as 10A IGN NO.2 so there ya go!

 

I am using IGN No 2 for my raptor lights to be always on. I am not very good with electricity. Is using IGN No 2 unsafe? If so , would you recommend another fuse to keep the raptor lights always on?

 

My fuse box