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Discussion Starter · #1 ·
Calling all electrical gurus!

I want to basically duplicate my dome light switch in the cargo area. So I want a slide or rocker switch that is off in the center with a different on option to each side; one for on and one tied to the door.

As I believe I mentioned in a different thread, I'm going to put an extra light in the cargo area. I want to have the option for the light to come on with the rest of the dome lights when the doors open, or to have it always on or always off. I'm hoping that I can just run a lead to each side of the dome light switch to another switch in the back.

I tried looking at some electrical sites. In trying to translate the electrical-speak I believe I need a double-pole double-throw switch like this one or this one. Can anyone verify that this is the correct type of switch?

Thanks!
 

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Both the dome and cargo lights work by "ground completion", that is, the light bulb always has power but needs a ground.

For the dome light, one position is fade-out ground controlled by the dome light ECU, the other position is constant ground, and the middle is Off.

So the switch you want is SPDT center off: that is, Single Pole (one circuit is controled), double throw (two positions or options), center off (in the middle, the circuit is interupted, ie, Off).

You'll need to replace the existing trunk switch with a new SPDT center off switch. One side will need a constant ground, the other will need a new wire run to connect with the 3-conductor ribbon cable that runs up the driver's A-pillar to the dome light. You can access this white cable with red stripes from behind the dashboard or by pulling the dome light. You'll need to tap off a wire in the 3-conductor ribbon (I forget which one of the 3 conductors) that provides ground when a door is opened.

I assume you know this will change the behavior of the cargo light. As supplied by Scion, the cargo light is independent of the passenger doors and only comes on when the cargo door (trunk) is opened.

BE CAREFUL: some people have fried their dome light ECU by shorting it out. A replacement is roughly $400.
 

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Suggested alternative: install a couple of LED strips at the tops of the C-pillars in the cargo area and slave them from the dome light contacts, such as they get power/ground when the dome light bulb gets power/ground. While you're at it, replace the dome light with a 9 or 12 LED panel (5050 type SMD is brightest).
  • Wiring and installation will be much simpler
  • you will have additional light in the cargo area when you open your doors
  • you can control that additional light with the existing dome light switch
  • you will retain the function of the existing cargo lamp
As always, have fun!
 

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Discussion Starter · #4 ·
What I, in my ignorance of electronics, had in my head was that there must be 3 wires going to the dome switch, so I would just run those same 3 wires to the back and connect them to another switch that then connected to my led's that I'm going to mount in the cargo area.

Maybe I will just run them from the cargo-light switch. At first glance that just seemed like a weird switch in that it actually swings one end of the bulb over so I thought it might be difficult to tap in to it. I'll take a closer look today.

BTW I already swapped out all of the interior lights with led boards from Oznium. They are so much brighter! The only one I sort of don't like is the one in the cargo area. Because it is on the side instead of from above, it kind of shines in my eyes. I might exchange it for something not so bright - especially if I have bright led's above.

Thanks so much for the info BrickPig. It is greatly appreciated!
 

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Maybe I will just run them from the cargo-light switch. At first glance that just seemed like a weird switch in that it actually swings one end of the bulb over so I thought it might be difficult to tap in to it.
That's what I did for the LED cargo lights that I added to the tops of my C-pillars. For power I tapped into the cargo light power wire. For ground I ran the ground wire inside the cargo light housing, where I "trapped" the bare end between the bulb end that moves and the metal contact. That way the new lights are on/off same as the OEM cargo light. I tried soldering the new ground wire but for some reason I couldn't make it stick to the metal.
 
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