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Illumination Circuit Woes

1021 Views 6 Replies 2 Participants Last post by  amarusrelor
Greetings folks.

I have a 2016 LE Rav4 that I really enjoy. Back in 2019 I decided to install aftermarket seat heaters for the cold German winters. Many thanks to AndSpenRob with his fantastic post (2012 RAV4 aftermarket heated seat installation (lot of...) helping me accomplish this. I differed in where I wired the switchs up though.

Power: Left & Right Accessory outlets (cigarette lighters) power wires
On: Left Acessory outlet power wire & Unused traction lock harness power wire
Ground: Left & Right Accessory outlets (cigarette lighters) ground wires
Night Light: Seat Heater switches (G26/G27), + illumination wires

The problem is that sometime after completing the mod (unsure of how long) I noticed the some of my interorir lights either no longer illuminated or were significantly dimmed. I have checked the dimmer and confirmed this wasn't the problem.
Lights that have been affected include: Cruise Control Switch, Steering Pad Switches (weak, but on), Combination Switch (Eco/Sport mode), Telltale Light (weak, but on), all three AC control switches (the center LED on the power circuit unaffected), and the shifter illumination light. Everything on the radio/nav head is perfectly fine.

I tested the bulbs in the AC switches and everything is working fine there. I also took some measurements on voltage/amperage which I can provide if helpful. I attached the wiring diagram below, but frankly the power and ground paths
Building Rectangle Font Parallel Engineering
running across multiple junction blocks are very confusing. I am at a loss on what I can do next for troubleshooting. I am thinking to test the Junction Connectors on the path of the lights that are out, but would welcome any inputs or thoughts.
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Have you tried to disconnect the heated switches to see if the interior lights come on normal again? Sounds like something might be pulling down your voltage. How did you confirm your dimmer is not defective? Hard to see the schematics but I would definitely look at the junction blocks.
Thank you for your questions and engagement. So I have tried without the heater switches connected and it doesn't affect the lights at all. I have even removed the heater switch illumination wire from the illumination circuit and it doesn't resolve the issue. This leads me to believe permament damage may have been done but I can't say for sure. The heater switches are wired into the 12V power outlets which are a different circuit than the illumination so I would think they can't affect each other.

One big question I have is what the voltage across the switches should be in a normal scenario. There was 11.4V across the fuse which I would expect, but only 2.5-2.6V (.003-.005A) across the illumination terminals at the switches. That makes me think a voltage drop is the culprit. The problem is that I don't have a solid understanding of the circuit because it is so complicated with J/Bs. I can't even say for sure where the various parts of the circuit go to ground. I will repost the circuit as a full file for legibility.

As for the dimmer, I think it's good because it still dims and brightens all the functional lights without issue, and I can see the change in resistance over the A/C illumination wires with my multimeter.


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G94 and G104 would be the junction blocks I would take a look at, these are the ones that appear to be related to one another. Maybe loose connection. The ones that appear to be okay seem to be powered by a different distribution block, so definitely take a good look at the ones I mentioned above
I will give that a shot next time I have time to pull off all the panels. I was able to get to G103 for some testing but it was very difficult to test the J/B. Am I correct in assuming that the voltage should be ~12V across everything in the ciruit? It doesn't look like there are any in series resistors that would drop the voltage but I don't know if those are typcically included on these diagrams. And I can't find in my digital manual what the nominal values should be.

I hadn't considered G104 but I will take a look. Hopefully it's easier to get to than G94 and G103. Thanks again Asantoyo4.
When I was doing some test to install some ambient lighting in my RAV-4, I believe the lowest voltage I saw with the dimmer all the way down was around 7 volts, and when the dimmer switch was to highest setting, the voltage was around 12, each switch assembly has the LEDs, diodes and resistors to turn down the voltage to prevent the diodes from burning up... at least this is my theory btw lol. If you were able to get to G103, it might be possible that G104 might be getting power from G103. So I would definitely visit those two blocks
Sounds good. I'll report back when I get results on it.
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