2021 Prime: Cabin Lighting Gone

2021 Prime:

Hello all. "<strike>THINK</strike> HOPE" I blew the dome light fuse. How? Replacing the rear seat bulb w/slightly larger LED bulb AND the light was on when replacing. All cabin lighting dead mid stream w/LED bulb replacement. This is a recently acquired (nearly mint) vehicle w/less than 25k.

FUSES BOX LAYOUT
Fuse box diagram Toyota Prius 50 51 55 (2015 - 2022) relay with assignment and location

• 19 and 1 are furthest to front of car
• 36 and 18 are closest to driver
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• Left row (19-36) appear to be accessory fuses only powered when vehicle is on.
• Right side (1-18) appear to be always powered. Center pole for power.


Photo of cabin fuse box untouched, and a few fuses were empty.

• #19: 7,5A FOG RR – Rear fog light
  Not equipped, no light on light probe when car is on.
  
  
• #08: 10A TAIL – Side light, rear fog light, front fog light, backlight
  Unclear ~ Side light turn signals in the mirror? If so, not equipped.
  Rear fog light ~ Not equipped.
  Backlight ~ what is that?
  Light probe shows light, always on
  
  
• #09: 20A DOOR – Window regulators
  Windows (and their respective buttons) seem to work fine? What are window regulators?
  Light probe shows light, always on

• #14: 15A WIPER RR – Rear wiper and washer
  Not equipped.
  Light probe shows light, on.

DOME FUSE
My understanding is it is a 7.5 fuse (brown,) which looks to be third from the top on the cabin fuse box lid (number 21 according to Toyota numbering.) If this fuse is removed, noticed no backup camera. Replace fuse, backup camera restored but still no dome light. Something else going on?
Fuse box diagram Toyota Prius 50 51 55 (2015 - 2022) relay with assignment and location

Observations for trouble shooting

• Cabin lights in general worked fine even when bulb was missing from rear dome light.
  
  
• When accessories are on, light probe lights up for every fuse EXCEPT 19-24, and 1-5;
  functions work fine so do not know why light probe does not light for these fuses?.
  
  
• Removal of fuse taps (see dash cam below) reflect no change.

DASH CAM FUSE TAPS
Including here as others have been posting unanswered questions on which fuses to tap...so to help anyone following even though the world has moved onto Gen5.

• #26: 15A RADIO – Audio system, monitor, navigation
  Accessory power wire
  
  
• #14: 15A WIPER RR – Rear wiper and washer
  Always on wire (parking monitor w/auto off battery protection.)

WILD CARD
Obviously, since the loss of light was immediate to the slightly oversized LED going into the rear dome light while the power and lighting was all on, this clearly looks like a blown fuse. That said the Dome Light fuse has been replaced and still not cabin lighting.

Few days back I installed recessed trunk lighting, tapped off the luggage light. This was all working just fine w/o issue. Including the context as possibility something else happened that would cause the cabin lighting to fail, and more of a coincidence to timing of flown fuse - or possibly something else got blown instead. Honestly though low voltage LED and wire (and we are talking about very small wire)

Also worth mentioning I'm a novice around auto fuses. I have the light probe, and a Kaiweets multi-meter, yet I'm not all that great with the meter even after all the Youtube rabbit holes.

What would you do next to isolate the issue?

 

"FWIW, be careful with those simple light probes; you can pop an ECU if you get on the wrong circuit path."

For real? Something so simple and effective? I'm ok switching to multimeter just need to know it better.

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Yes, tried reverting back to incandescent bulb however the replacement (tried two different types, both slightly larger) stretched out the connector a little so old bulb falls right out. NOW, my thinking here is that the other lights should work either way - nothing requires the back seat dome to run.

Yes, tried anything to get any light to work on its own... in all switch positions (driver dome, read dome, luggage light in trunk) - and jumping the bulb.

 

I was keeping the clip grounded and hunting for ACC and 24/7 power and dead fuses. Can't find a dead fuse, don't understand why the cluster of fuses listed above don't light the probe up, and have no interior lighting. Took the car for a drive and everything else seems unaffected. Do not think it would be a short per-say (I mean, I can't imagine anything broke or got pinched.) That said, these are about the thinnest wires I have personally seen - these light wires...hope I didn't break something?

Would you know of ways to test (ie continuity) to determine the light wiring itself is ok? I'm puzzled no doubt, and this is all after I thought I was out of the woods... project was wrapped up and done...just to put in that forgotten LED.

 

No bulb in there atm - and appear to have lose the hybrid system so problem expanded. Think a reset should restore the hybrid system, then back to the lighting issue. Thought LED auto bulbs 'didn't' have polarity?' Nothing on the bulbs I can see indicating one side from the other (talking all cabin bulbs that were replaced w/LED. Doubt they were all done randomly correct. The passenger bulb was the only 'odd' one that required a special order (never understand things like that ... where all bulbs are identical but on odd one out. CAn't see a single reason why the rear cabin dome light would require a different dome bulb than rest of the car - or why it couldn't match the front dome light bulb.)