TUTORIAL: Wiring accessories to interior fuse box with add-a-fuse tap

[Brad666]

What size if fuse tap that you used micro #2? I want to buy everything ahead of time

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[SPITmadFIRE]

What size if fuse tap that you used micro #2? I want to buy everything ahead of time

Fuse taps only differ based on the size of the fuse you're trying to install, as far as I know. If you got a Micro2 fuse tap, it would probably work for most of the fuses you're trying to tap into in the interior fuse box.

What are you trying to wire up? Again, my specific purchases won't help you because they were for my dashcam setup and wouldn't work with any other sort of accessory unless it runs off the same wattage and plug.

 

[Brad666]

aux bumper lights

 

[SPITmadFIRE]

aux bumper lights

You're looking at an external accessory, not an internal accessory. I wouldn't recommend using an add-a-fuse tap for external accessories, because your best bet is to use a relay wired directly to the battery instead. This thread is strictly about interior accessory wiring which is much easier.

 

[Brad666]

OK but I cannot wire it to a switched source that way, meaning if switch is left on lights are left on I get wiring it to the battery and ground is simple and easier... thank you for your help

 

[SPITmadFIRE]

OK but I cannot wire it to a switched source that way, meaning if switch is left on lights are left on I get wiring it to the battery and ground is simple and easier... thank you for your help

It's not safe to wire external accessories to the internal fuse box -- they're separated by the engine bay firewall for a reason.

To be clear, I would never recommend wiring an accessory directly to battery and ground. The safest and easiest way to wire an external accessory is using a switched relay. Whether you switch that relay with an actual physical switch, or with another power source, doesn't really matter. I would never add-a-fuse in the engine bay fuse box for fear of losing power to some critical system while driving. If my interior add-a-fuse goes wrong somehow, the worst thing that happens is my 12v socket / wireless charger go out.

 

[Brad666]

Ok thank you for your help . I have a wiring harness with dual switch and in line relay
It would need to be wired to the battery and ground to work. Thanks again

 

[SPITmadFIRE]

OK but I cannot wire it to a switched source that way, meaning if switch is left on lights are left on I get wiring it to the battery and ground is simple and easier... thank you for your help

For example; wiring up a high-draw accessory like a compressor would go like so:

ACCESSORY (+) <-- RELAY <-- FUSE <-- BATTERY (+)
   (-)              ^                  |
    |               |                  |
    |             SWITCH (+) <----------
    |              (-)
    v               |
  GROUND <-----------

 

[SPITmadFIRE]

Ok thank you for your help . I have a wiring harness with dual switch and in line relay
It would need to be wired to the battery and ground to work. Thanks again

Yeah, if you have an inline relay, fuse, and switches already, then you should wire that directly to the battery and ground -- if you're not familiar with automotive wiring work, I would recommend against doing this sort of thing yourself. It's something a mechanic or aftermarket installer could do pretty quickly (and safely!)

 

[Brad666]

I am familiar was looking for an easy clean way to pick up switched power, thank you

 

[da_jokker]

I recently used an add-on tap for the first time. Even though I've been wiring things in vehicles for years, But never buy tapping into the fuse box.

Anyway, something I learned was that at a fuses have a specific direction. You cannot install them any direction you want. The way to tell if you did it right, is if you pull one of the two fuses, the other side should still be powered. If you pull 1 fuse and loose power to both, you're upside down.

 

[GunninGopher]

I recently used an add-on tap for the first time. Even though I've been wiring things in vehicles for years, But never buy tapping into the fuse box.

Anyway, something I learned was that at a fuses have a specific direction. You cannot install them any direction you want. The way to tell if you did it right, is if you pull one of the two fuses, the other side should still be powered. If you pull 1 fuse and loose power to both, you're upside down.

For a minute I thought that you were saying that fuses acted like diode's. I then realize that you are talking about which fuse you use in a tap. Yes, one fuse in the tap fuses both circuits, while the second is for the added circuit. I would test for the primary by seeing which has power before installing fuses, which would indicate the primary fuse.

 

[GunninGopher]

I wired directly from the battery for my auxiliary brake system for my tow set up. I need constant hot and the 12v outlets shut off after less than one hour. I would have preferred an add a fuse, does anyone know what slots are constant hot without the timed shut down?

On another thread that discusses all about flat towing (worth the time it takes to read all 25+ pages), someone recommended #29. I tested it and it was hot while the Bronco was off, but I didn't time it to see if it was on a delay. I doubt it is because that post was from weeks ago. I'm completing the install this weekend and will test it on a road trip next week.

The biggest issue about the TOAD braking system I've seen right now is the 6cyl brake booster stays on for about 30 minutes then shuts off. We have a 4 cyl, so it isn't an issue for me.

 

[da_jokker]

For a minute I thought that you were saying that fuses acted like diode's. I then realize that you are talking about which fuse you use in a tap. Yes, one fuse in the tap fuses both circuits, while the second is for the added circuit. I would test for the primary by seeing which has power before installing fuses, which would indicate the primary fuse.

Actually I may be. There's actually a proper direction when you install a add-a-fuse. Literally meaning point to left or pointing to the right.

If you plug it in to the fuse box the wrong way, it will not properly protect and does not "separate" The two circuits.

For exame, say you put a 5A and a 20A fuse in. If you plug it in the proper orientation, You will get two separated circuits with protection matching their fuses.

However if you put it in upside down circuits are actually using the 5A fuse and can blow that one when you try and power up you 20A device.

As I mentioned, the easy way to test is to pull one of the fuses and verify the other circuits still has power.

 

[GunninGopher]

Actually I may be. There's actually a proper direction when you install a add-a-fuse. Literally meaning point to left or pointing to the right.

If you plug it in to the fuse box the wrong way, it will not properly protect and does not "separate" The two circuits.

For exame, say you put a 5A and a 20A fuse in. If you plug it in the proper orientation, You will get two separated circuits with protection matching their fuses.

However if you put it in upside down circuits are actually using the 5A fuse and can blow that one when you try and power up you 20A device.

As I mentioned, the easy way to test is to pull one of the fuses and verify the other circuits still has power.

I see what you are saying. I was reacting to the statement "fuses have a specific direction" that gave me the impression that a fuse itself acted as a diode which, of course they don't.

I'm also a noob at using these taps. I've usually just ran separate switched or relayed circuits in automotive installations. When I was younger I would add a jumper to the hot side of a fuse once in a while, but that isn't something I do these days. This is the first time I've used a tap like this and that is a good thing to check out. I don't want to draw any more power through that fuse slot that it is originally rated for, so I'll ensure that it is oriented correctly, as you suggest.

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