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I own an old Maruti Suzuki WagonR (2009) which is not having a dome light in passenger area. I want to install a LED light there but can't locate the power cable coming from battery. Since the car is old, I don't have its manual (though I doubt such technical details are mentioned in user's manual) I tried to search on internet for a circuit diagram but can't find one.

Can you please point me in right direction?

P. S. Its having a dome light in driver's area but its not useful for the passengers sitting in second row.

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On most vehicles, the entire dome light assembly can be removed, or the cover popped off so that the bulb can be changed. You should be able to carefully pop it out and gain access to the light bulb and wires.

Most dome lights have three wires:

  • constant power
  • power when the door is open
  • ground

There is usually a 3 position switch. When the switch is in the default position, the power from the door open circuit allows the light to come on when the door is open. When the switch is moved to full on, the constant power keeps the light on. When the switch is off, the light will never come on. The ground is used as the return in all scenarios when the light is on.

I would extend these 3 wires to your new location, and use them for your new light as well. That way the light will come on when the existing light does. You could optionally include your own 3 way switch to have the front and rear lights permanently on/off independently of each other.

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  • Thats what I did. Just extended the existing dome light wire to the new location. What actually I was trying to do is to have a new and independent connection for my custom fitted LED dome light series but didn't find the power connection. Now, I will try to use the cigarette lighter connection (also use for mobile charging) to achieve the same. :) – Mudassir Dec 9 '17 at 4:23
  • @Mudassir, same idea, except going to the cigarette lighter is the same as the existing dome light. There should be a constant 12v power wire in your existing light. Thats how it's able to turn on even without the keys in the vehicle. Double check the power at the cigarette lighter. On a lot of vehicles, this circuit isn't active all the time. It's sometimes only when the key is turned to accessory, or for X amount of minutes after the vehicle is turned off. This would disallow you from using the light except in those conditions. – raydowe Dec 11 '17 at 8:48
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    Yep, cigarette lighter is not having power when the keys are switched off :) – Mudassir Dec 11 '17 at 9:08
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Take the existing light out and test, using a test lamp or multimeter, each of the wires to find the one that is live.

This does assume that the existing lamp is working otherwise you need to check the supply.

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  • Car is not having any connection in passenger are, so there exist no existing light :-) Sorry, if my question caused the confusion. – Mudassir Dec 5 '17 at 7:29
  • You have an existing light - extend the supply from that - this also means it is controlled by the door... – Solar Mike Dec 5 '17 at 7:34
  • I want a direct connection from battery (via fuse box). Want install multiple switches in between so that all the rear lights don't depend on door controlled front light switch. – Mudassir Dec 5 '17 at 7:41
  • You don't need a new power source for that. The dome light in the front will have constant power, so it can be turned on even when the car is off. Forwarding the connection from the front dome light is the easiest way to do this. – raydowe Dec 5 '17 at 13:22
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chrisfix has done a very good video on how to install an auxilary light. youtube link

the only difference is in your case the lights are going to be inside.
basically you need to do these

  1. Find out the wattage of the lamps
  2. Create fusible wire link with proper ohmage calcuated from lamps wattage
  3. Find a way to move your wire from under the hood to inside and its expected length, then buy wire according to that length (I think you might need 1.5mm^2 wire)
  4. Use a relay if your LEDs are of high wattage and thus you can bypass high current flowing over your head.
  5. Create a rough diagram of what you need to do
  6. And last but not the least before doing any modification Disconnect negative terminal of the battery
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  • Really a great video. – Mudassir Dec 9 '17 at 4:18

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