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Holy grail blade fuse box installation E28

Upgrading my E28 fuse box to blade fuses using the Holy Grail fuse box.

learning context

Older BMW were originally equipted with Bullet style fuses, these fuses are not redibly available in local autoparts or dealerships. As the years pass and our vehicles get older it is wise to upgrade your fuse box to the new blade style fuses which are redible available everywhere. The fuse box is also known as the power distribution box in wirring diagrams, think of your fuse box as the electical heart of your car. The fuse box directs power to all parts of your car when you turn soemthing on like your headlights or A/C. A bad or poor working fusebox can casue intermitent electrical issues that can keeo you from enjoying your car.

Symptoms of a bad fuse box

  • Loose fuse terminals
  • Melting on fuse terminals
  • Fuses blowing frequently
  • Intermitent electrical issues

Reason for upgrading my E28 fuse box

I decided to upgrade the fuse box in my 1987 535I BMW becasue I was experiencing electrical issues that are casued from loose fuse terminals. As well as intermitent no 12V to fuse 1 which is part of the starting circuit.


  • Remove the old fuse box
  • Use a notebook and a lot of pictures to aid in the installation of the new fuse box.
  • Parts/Tools
    • Holy grail fuse box
    • Phillips screwdriver
    • Flat screwdriver
    • Needle nose pliers
    • 10MM socket
    • Notebook and pen


  1. Disconnect your battery. Before you do any work on the electrical system on your vehicle always disconnect the 12V battery to reduce any risk of shorting out an electronic device on your vehicle. I removed my battery completely and used a trickle charger to charge my battery.
E28 12V battery shelf

2. If your car is equipped with cruise crontrol, it is best to remove it while working on the fusebox. The cruise control unit is helt by three 10mm nuts.

3. Remove all of the fuses and relays from the fuse box, I advice to take many pictures. I took allot of pictures and wrote notes down and still encountered problems while putting everythign together.

4. Remove the two phillips screws that hold the upper and lower fuse box together. Do not remove the offcentered L wrench bolt, this bolt screws the power supply from the battery to the fuse box.

5. Once you remove the two bolts, lift the top of the fuse box off the base. The top part of the fuse box is help by three presure clips, you can remove it by genlty pulling on the four corners one at a time. To get more space, remove the harness from the clip up against the engine bay wall. As well as pulling the rubber seals from the lower fuse box.

6. Remove the two 13MM nuts that hold the bottom half of the fuse box. This gives you more space to be able to manuver the fuse box while you work on it.

7. Once you remove the bottom half of the fuse box, turn over the fuse box and take pictures of what cable colors are connected to what pins. This is a good time to take a look at your cables and look for any heat damage.

8. After taking pictures and notes, use the needle nose pliers to disconect the cables from the back of the fuse box. One tehcnique that i used to keep track of the ables, I wrapped masking tape on the cable and labeled it with the pin.

9. After removing all of the connections, take a flat head screwdriver and remove the fuse tabs from the fusebox.

10. After removing the fuse box tabs I noticed that fuse 17 had some heat damage, this could be casued from a bad fuse tab. This one reason why to upgrade to the new style fuse box.

11. Take some side cutters and cut the plastic tubes from the base of the sufe box to allow the new insert to slide on. You do nto need to cut them completely flush, but do cut them as close to flush as possible.

12. ONce you remove all of the tabs, take some non conductive lubricant like WD-40 and spray the back of the new fuse box to help it slide into the housing easily. While installing the new fuse box you might need to adjust pins that are not lining up with the slots in the top fuse box housing. I had to adjsut a few blades and spent abotu 10 minutes installing the fuse box.

13. Once you install the insert, reconnect all of the pins in the back. Go back through your pictures and notes to reconnect the fuse box.

14. If you have issues reconnecting your fuse box like I did, I reomcend you cheking out the pictures that Holy grails has of the sample fuse box. It helepd me allot when I had mixed a few cables.

15. Once you have confirmed that all of your cables are hooke dup properly, take the ground cable that is included with the fuse box and slide it throught the rubber seal. I ended up bolting it to the negative terminal on the battery, but you are able to hook the ground cable to the ground bolt on the right side of the battery.

16. Once you hook the ground up re install the upper and lower fuse back together and reinstall the two phillip screws that were removed at the beginning of the repair.


This upgrade is daunting but well worth the time, it took me two hours to isntall. The hardest part for me was the reconnecting of the cables, as I had gotten a few pins mixed. Once I got past that part everythign else was easy, the lights you are able to switch on and off

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