Great update! To your question, Maybe a safety feature that's why voltage goes out? Or a heater timer feature? May i ask which pin did you tap power from the window switch itself to illuminate the window switch? Thanks!I couldn't stop thinking about this. So got a 2018 C-HR passenger window switch w/illumination off of ebay as it was only $28. I chose the C-HR as my Master Window Switch is from a C-HR so to keep it consistent looking (with the silver accent trim and "A" icon).
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Since it came from ebay, I wanted to verify the switch will illuminate if I supply power to Pin3 and GND to Pin1.
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I proceeded to tap into the rear heater switch to provided the missing Pin1 and Pin3 on the window harness.
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And that is where things starts to get confusing (at least for me). The window switch would illuminate as expected with the headlights on, as well as with the car in Acc. However, with the car Ignition On, the illumination goes out even though the rear heater switch stays illuminated. So tried to map out the voltage state of the rear seat heater pinout (as I can't find it online) and it makes no sense to me why there is no voltage between Pin6 and Pin5(GND) when the Ignition On, and how does the rear seat heater switch can stay illuminated in that case. Unless the rear seat heater illumination is powered a different pin in the harness but I don't know how that can be when only Pin6-Pin5 has power when headlights are on. I might be totally wrong about this so if someone out there understands what's going on or has a pin-out for the rear heater harness please reply.
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Long story short...I give up trying to power the passenger switch illumination via the rear seat heater. Instead, I just tapped power from the window switch itself. In this case, the window switch illumination will be on whenever the ignition is on instead of being in sync with the headlights (which would have been nice). I might go back and rewire it if someone has figure out how to sync it with the headlights on/off.
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