[jmciver]

So I was doing a little recon of the trunk fuse box in preparation for installing a few aftermarket electronic accessories. Prior to the recon, I searched the net for info on the best fuses to tap for constant and switched 12V - and I found some decent info with most using the "add-a-fuse" method. Then I stumbled across a professional install where an unused fuse spot was used without an add-a-fuse or splicing into existing wiring. After a little more investigating I found out just how ridiculously easy it is to tap into power in the trunk fuse box the way the factory does it - very clean, no wire taps or add-a-fuse (and I was surprised my searches did not find much on this OEM method). Below is what I found out and should be applicable to hardwiring any aftermarket accessory.

So why do this instead of just using the very popular add-a-fuse method? Well for me, my OCD prefers an installation looking as OEM as possible - even the wiring. And fortunately, the rear fuse box makes it very easy to access the bottom of the fuse box and the individual terminals (easier than any other fuse box I have worked with in previous cars).

Note: While this should be applicable to most F8X/F3X cars, there may be some differences based on installed options in different vehicles. However, once you take a look at your fuse box as I did below, it should become obvious how much flexibility you have to work with in the fuse box in your car. And of course, be sure to disconnect the negative terminal on the battery before you start messing around with the fuse box.

This first pic is the rear fuse box. The yellow circle in the upper left are the fuses in question that have power going to them, but are not actually connected to any equipment in the car. Those three fuses, and the other three fuses that make up the group of six, are all on with ignition, and off when the ignition is off (these fuses do not stay on for ~10 min after the ignition is turned off). From top to bottom, these are fuses 143 thru 148 (143-145 are unused in my car even though there is a fuse installed in these spots).



The next pic is the bottom side of the fuse box. Each of the fuse groups you see from the top are connected to the colored sockets you see here. The brown socket in the lower left is the one I will be working with, which houses the fuses I mentioned above.



Here is a pic with a closeup of the brown socket removed. To remove the socket, you need to remove a red plastic "pin" which will release the socket (seen in the pic above). I removed this red plastic pin with a simple pick tool. You will notice that only three of the sockets have wires in them from the factory.



After doing some parts research on RealOEM, I found the terminal plugs that are used inside the fuse box. It was difficult to know for sure that the ones I found would work, but I decided to take a chance since they were not that expensive. Part Number 61130007438 is the part number I chose. This is the one that has ~9 in of wire already crimped - I chose this one because it was more convenient. I say not that expensive, but they are not that cheap either for what they are. Expect to pay $2.50 - $4.00 each for these little puppies. I bought mine from FCP Euro.



The terminal pin slides in and snaps into the socket. The pic below shows the new terminal pin with wire (blue/black wire) inserted, and the socket installed back in the bottom of the fuse box.



This last pic is the fuse box re-installed, with the new wire (blue/black) routed under the fuse box and then around to the back of the fuse box temporarily. I routed the new wire via the same path as the bulk of the other wring under the fuse box. Since I did not want a "live" wire just sitting there until I install my accessory, I removed the fuse and put it in one of the spare fuse holder spots - it is the brown 5A fuse in the upper right.



The beauty of this setup is that when I install my accessory, I will use a fuse that is the proper size for the accessory. I left the other two spots in that bank of six fuses open for now, but plan to use them for some other aftermarket accessories in the near future - each with their own circuit and appropriately sized fuse.

The last thing I did during my fuse box recon mission was to find out which fuses were a true constant 12V with the ignition off AND the car is "asleep" (i.e. the ~10 min after the ignition is off when most of the circuits finally shutdown). You will need to refer to your fuse box diagram located in the trunk fuse box. Here is what I found (you should also double check with a voltmeter or circuit tester before you actually use a circuit):

The following fuses are constant 12V: 100, 103, 104, 106-109, 112-114, 116, 117, 120, 123, 149, 150, 160, & 161

The following fuses are on AND off with ignition: 143-148, & 154 (143 is the one where I added the OEM terminal above)

The remaining fuses are on with ignition and then remain on for ~10 min after the ignition is turned off, and then turn off.

Other things I noticed while poking around:

1. Fuses 109, 112 & 125 are blank, meaning that there is no fuse installed in the spot, but a fuse could go there. There are other spots that don't have fuses, but these spots can't have a fuse installed since there is no terminal connection to the power bus inside the fuse box.

2. Fuses 112-117, and 136-142, do not have sockets installed. Presumably these are for special option equipment. In theory, you could purchase the applicable sockets and the corresponding terminal plugs to use these fuse locations to power other accessories.

Hopefully you will find this info helpful. Especially for those with OCD like me who like to have clean, OEM-like installs - even with the stuff that is not actually seen when your accessory is installed .

[ian332isport]

That's an excellent write up

It's a shame you didn't post it sooner though. I've been through a similar process, and even bought a used rear fusebox to see exactly how things are connected. It's amazing how many of the installed fuses actually do nothing.

We mush have similar OCD issues. I hate to see anything that doesn't look OE on my cars.

[jmciver]

Originally Posted by ian332isport

That's an excellent write up

It's a shame you didn't post it sooner though. I've been through a similar process, and even bought a used rear fusebox to see exactly how things are connected. It's amazing how many of the installed fuses actually do nothing.

We mush have similar OCD issues. I hate to see anything that doesn't look OE on my cars.

Thanks! My OCD has a habit of making extra work for me when it comes to my cars - I have also bought used parts to "see how things work" too, before actually putting my car under the knife for an install. After doing this bit of research, I can't help but wonder if BMW left those 3 unused fuse spots (143-145) open on purpose as they conveniently have 5, 10 and 15 amp fuses already there, ready for use.

[ian332isport]

You can see what does what here:

https://www.newtis.info/tisv2/a/en/f...-rear/KZX1sxlx

143 is only used on convertibles
144 & 145 are only used in Diesel powered cars.

[jmciver]

Originally Posted by ian332isport

You can see what does what here:

https://www.newtis.info/tisv2/a/en/f...-rear/KZX1sxlx

143 is only used on convertibles
144 & 145 are only used in Diesel powered cars.

Interesting... I never bothered to look that far after I found what I needed . Although, I figured fuse 143 had something to do with a convertible based on the fuse box paper schematic included with the rear fuse box.

[Read-This]

Really appreciate the effort of this post, thank you!
To add, I too wanted the OEM look and went about my work in a similar route.

I purchased a 'used' rear fuse distribution board [which included its wiring loom plugs] from a well-known auction website [I paid £20 UK Pounds].

I needed a blue wiring loom plug to connect to the constant live fused ports numbered 112-117 for my F34. Each loom plug is unique to each port of the board 'however' by trimming the raised plastic keyway of the loom plug, they will fit elsewhere in similar shaped port.

I also re-used the existing pins of my purchased blue wiring loom plug by carefully de-pinning the loom plug, soldering the new wire and re-pinning the loom plug.

[4kncld]

This is really well written. I'll be hardwiring a dashcam for a 440i gran coupe and I'm praying the fuse set up is the same as yours so I can follow these steps

[erickonphoenix]

What a great write up! Many thanks!

I'm not sure the ALP or the Valentine would reach the trunk but the dashcams will definitely reach. I'd also like to get my police scanner hardwired this way as well. Thanks again.

[jmciver]

Originally Posted by erickonphoenix

What a great write up! Many thanks!

I'm not sure the ALP or the Valentine would reach the trunk but the dashcams will definitely reach. I'd also like to get my police scanner hardwired this way as well. Thanks again.

Sure they could, just need to extend the wires as necessary and run them to the trunk - very easy to do. I needed to extend my dash cam wires as well (which I documented in another thread). I also did it with my V1 install, even though my V1 is installed in the rear headrest.

[samsamdar]

Does anyone know where I could find replacement colored connectors? I'm currently looking for a teal colored 7 pin connector that would go into the top right slot...

[jmciver]

Originally Posted by samsamdar

Does anyone know where I could find replacement colored connectors? I'm currently looking for a teal colored 7 pin connector that would go into the top right slot...

Check eBay for used F3x/F8x fuse boxes, or a local salvage yard...

[Read-This]

Originally Posted by samsamdar

Does anyone know where I could find replacement colored connectors? I'm currently looking for a teal colored 7 pin connector that would go into the top right slot...

...If you are unable to source the port plug second hand, providing you have the part number [of the port plug] BWM will order it for you.

From my initial post further up the thread, I purchased second hand the complete rear fuse board that included various port plugs [£20 UK pounds]

[samsamdar]

Originally Posted by Read-This

...If you are unable to source the port plug second hand, providing you have the part number [of the port plug] BWM will order it for you.

From my initial post further up the thread, I purchased second hand the complete rear fuse board that included various port plugs [£20 UK pounds]

Do you know where I can find the part numbers for any of the port plugs?

[ian332isport]

Originally Posted by samsamdar

Do you know where I can find the part numbers for any of the port plugs?

Although BMW are pretty good at supplying a lot of connectors, they don’t sell every single one.

I don’t think you’ll get the port plugs for the fuse box. Those would probably only come as part of a complete loom or retrofit kit. They do sell the individual contacts for repairs though.

As above, you’ll need to find a used one.

[TouringM3]

Yo jmciver
I know i'm really raising this thread from the depths, but do you happen to know / recall if I could simply pop a 40A fuse into locations 109 or 112 and be in good shape - or are they only capable of certain amperages?


Thanks!

[jmciver]

Originally Posted by TouringM3

Yo jmciver
I know i'm really raising this thread from the depths, but do you happen to know / recall if I could simply pop a 40A fuse into locations 109 or 112 and be in good shape - or are they only capable of certain amperages?


Thanks!

Difficult to say as amperage limits are not only based on the equipment being powered but also the thickness (or gauge) of the wiring connecting the equipment to power. The battery feeds the main bus bar inside the fuse box, with a thick cable, which can handle the total amperage draw of all components connected to the fuse box. So in theory, as long as you connect wiring from that fuse location (which should not have any wiring since IIRC that fuse is not connected to any components in the car), to your new component using appropriate gauge wire for 40A, you should be fine.

[TouringM3]

Originally Posted by jmciver

Difficult to say as amperage limits are not only based on the equipment being powered but also the thickness (or gauge) of the wiring connecting the equipment to power. The battery feeds the main bus bar inside the fuse box, with a thick cable, which can handle the total amperage draw of all components connected to the fuse box. So in theory, as long as you connect wiring from that fuse location (which should not have any wiring since IIRC that fuse is not connected to any components in the car), to your new component using appropriate gauge wire for 40A, you should be fine.

OK awesome, awesome.
Both of these gauge wires are largeish (4.0 / 2.5), so i'd be sure that the proper wire is still used.

Images attached. 4.0 is the power tailgate, 2.5 is the active rear diff.

So my game plan will be to slam a 40A fuse into 109 or 112, use the proper leaf-spring lead into the back of the fuse block, and prepare myself for locked-diff donuts while opening and lowering the power tailgate. (jk)

[jmciver]

Originally Posted by TouringM3

OK awesome, awesome.
Both of these gauge wires are largeish (4.0 / 2.5), so i'd be sure that the proper wire is still used.

Images attached. 4.0 is the power tailgate, 2.5 is the active rear diff.

So my game plan will be to slam a 40A fuse into 109 or 112, use the proper leaf-spring lead into the back of the fuse block, and prepare myself for locked-diff donuts while opening and lowering the power tailgate. (jk)

Glad I could help. But out of curiosity, what aftermarket electrical component do you want to add that draws 40A anyway?

[TouringM3]

Originally Posted by jmciver

Glad I could help. But out of curiosity, what aftermarket electrical component do you want to add that draws 40A anyway?

Power rear liftgate

Turns out both the power liftgate in the F31 and the active rear diff in the F80 use the same fuse location, so when combining to make a fully functional F81, i need both to function with 40a fuses.

[AlmondJayRoM3]

Thanks for this. I’ve been using add-a-fuses on my F80 and G01 thinking they would only be temporary but could not find the right terminals. That part worked perfect for both cars.

[mentbase]

Hi jmciver,
Based on your experience, is it possible to insert the wiring connector (Part Number 61130007438) into the socket without its removal (that whole thing secured by the red plastic "pin")?
Thank you!

[jmciver]

Originally Posted by mentbase

Hi jmciver,
Based on your experience, is it possible to insert the wiring connector (Part Number 61130007438) into the socket without its removal (that whole thing secured by the red plastic "pin")?
Thank you!

I never tried it like that as it is very easy to remove the plug. But it possibly could work that way.