Negative or Positive Dome Light Switching?

[wolfpack1298]

I am installing a new overhead LCD and DVD system in my 2007 Tahoe. The manual indicates that there are two kinds of dome light circuits (Positive switched and Negative switched). I have to set the polarity switch on the unit when I install it, but I don't know what the setting should be for my vehicle.

Does anyone know if what type of dome light switching is used for the 2007 Tahoe?


Here is the actual section in the manual that discusses the switch types:

The dome lights in the video monitor require three connections to the vehicle's wiring. There are two common types of dome light circuits used, positive or negative switched. Positive systems supply voltage to the interior lights to turn them on, negative switched systems apply ground to illuminate the bulbs. To determine which system you have you must locate the wires at the dome light. On a positive switched system, with all the doors closed and the lights out, both wires at the dome light will rest at ground. When the light is activated, one of these wires will switch to +12 vdc. This is the vehicle's switching wire. On a negative switched system, with all the doors closed and the lights out, both wires at the dome light will rest at + 12vdc. When the light is activated, one of these wires will switch to ground.
This is the switching wire.

For positive systems, connect the purple / brown (Lamp auto) wire to the vehicle's switched wire. Then connect the red / black (lamp on) wire to a fused constant 12 volt source and the black / red (lamp common) wire to a good ground. Positive systems are commonly found on Ford vehicles.

For negative systems, connect the purple / brown (Lamp auto) wire to the vehicle's switched wire. Then connect the red / black (lamp on) wire to a good ground and the black / red (lamp common) wire to fused constant 12 volt source. Negative systems are commonly found on General Motors and import vehicles.

 

[wolfpack1298]

I found the answer!

I called a buddy who works as a tech for GM and he called me back. He told me that the switching is Negative.

 

[yourgmsolutions]

I found the answer!

I called a buddy who works as a tech for GM and he called me back. He told me that the switching is Negative.

your buddy is wrong. dome light trigger is positive and it's grey with black stripe wire

 

[wolfpack1298]

Hmmm.....

Well, I installed everything yesterday and the polarity switch is set to negative. The unit powers up fine.

I did notice that the dome light integrated into the overhead unit does not come on when the door opens. It has 3 settings (On, Off, and Door). If it's set to Door, the lights only come on when the key is in the ignition and turned on. The lights remain off if the door is opened, but the other doom lights come on in the front and rear of the vehicle.

Would the incorrect polarity switch be causing this problem or would I expect to see the unit not even turn on if the polarity was wrong?

 

[wolfpack1298]

I replaced the old unit with a new Valor overhead unit. The original Audiovox unit had a seperate power adapter connection (Red and Black Wire) in addition to the factory dome light wires (Orange, Gray, and Black).

The new Valor unit has 4 wires and I have included the descriptions directly from the installation manual.

1. Battery + lead (Yellow)
To connect the positive terminal of the car battery.

2. ACC Power Lead (Red)
To ACC power lead powered when engine key position is ACC.

3. Ground Lead (Black)
Connect the lead to a good chassis ground on the car. Make sure the connection is made to bare metal and is securely fastened.

4. Door wire
This lead is to be connected to the door pin of the vehicle. This allows the dome light to be switched by opening or closing door.

For my installation, I connected the Yellow wire to the red contant wire used by the original Audivox unit. I connected the black wire to the black ground wire used by the original Audiovox unit. I connected the Red Valor wire to the orange dome light wire. I connected the Valor Door wire to the gray dome light wire. The black dome light wire was not used.

The valor unit has a polarity switch, which is currently set to negative on the unit.

Based on this configuration, is the wiring correct and I simply need to change the polarity setting or is everything correct?

Thanks!