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Discussion Starter #1 (Edited)
T8 (USA) Rear Fuse Box - Adding a new circuit

After hardwiring my Radar Detector & DashCam to the passenger-area fuse box, I decided to have a look at the rear (cargo) area fuse box. The passenger area fuse box was completely populated, even for features not installed in my car. The rear fuse box, however, wasn't. Only circuits actually installed in the car are fused; the other positions are blank. That doesn't keep you from using these unused positions, however, so if you're interested in learning a quick way to add a 5/10/15A circuit in the cargo area, like for a rear-facing DashCam, read on - I might save you some time.

First, here's the fuse reference from the owner's manual:


  1. Heated rear window 30A
  2. Power rear seat (driver side) [Excellence] 20A
  3. Pneumatic suspension compressor 40A
  4. Rear electric heater (passenger side) 30A
  5. Empty
  6. Rear electric heater (driver side) 30A
  7. Power rear seat (passenger side) [Excellence] 20A
  8. Empty
  9. Power tailgate 25A
  10. Power front seat (passenger side) module 20A
  11. Trailer hitch control module 40A
  12. Seat belt tensioner module (passenger side) 40A
  13. Internal relay windings 5A
  14. Empty
  15. Foot movement detection module for opening the power tailgate 5A
  16. Empty
  17. Empty
  18. Trailer hitch control module 25A
  19. Power front seat (driver seat) module 20A
  20. Seat belt tensioner module (driver side) 40A
  21. Parking camera 5A
  22. Empty
  23. Empty
  24. Ionic air cleaner [Excellence] 5A
  25. Feed when ignition is switched on 10A
  26. Airbag and seat belt tensioner modules 5A
  27. Cooler; heated/cooled cup holder (rear) [Excellence] 10A
  28. Heated rear seat (driver side) 15A
  29. Empty
  30. Blind Spot Information (BLIS) 5A
  31. Empty
  32. Seat belt tensioner modules 5A
  33. Emission system actuator 5A
  34. Empty
  35. Empty
  36. Heated rear seat (passenger side) 15A
  37. Empty

Second, here's an annotated picture of the T8 (USA) Rear Fuse Box, showing installed fuses, which contacts are hot during following ignition (RED squares), which contacts are "always" hot (PINK squares), and which contacts in the fuse slots have no metal contact (YELLOW "X"):


Finally, this last picture shows how to properly install the Lumision FuseTap into position #24 (Ionic Air Cleaner), resulting in a now useful circuit that follows ignition:


Some ideas for using this circuit:

  • 12V Power Outlet that turns off with the car
  • Inverter for the rear seats, you know, like the one Volvo promised me would be installed in my T8 that WASN'T... :mad:
  • Additional external lighting effects
  • Hardwired rear-facing DashCam
  • Chilled (or heated) box for food, drinks, grocery, etc...
  • Magnetohydrodynamic Drive module
  • Flux Capacitor
  • Turbo Encabulator
  • Incinolet Electric Toilet
If you needed an "always on" circuit, you could rotate the FuseTap 180° and plug it into position #14 (currently empty).
Anyway, hope that this info saves someone some time.

Cheers,

SonarTech
 

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Thanks,
I have a late 2021 XC90 and tried using this diagram.
When testing my fuses with a circuit tester, I get constant light ups from the ones you denoted as SWITCH and then when I turn on my engine, NONE of my fuses light my circuit tester.
It's super weird and I don't know what's going on.
Anyone else have this issue or know what's happening?
 

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I am interested as well :) I honestly would rather just run 2 primary dash cams and use the fuse box in the rear so that I don't have to run any cables from the back of the car to the front.
So I am very interested in learning about how we can use the rear fuse box...I am in a '21 T8
 
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