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Internal car light switch replacement

TheOtherShiny

New Member
In the center of the roof in my car there is an OEM combined light and switch unit, the normal type which has 3 positions OFF - ON and ? (I don't know the name for it, but it turns on if you insert the key or open the door.

OFF - always off, even when the door opens
ON - always on, overrides any other signals, turns other lights on too.
? - turns on if you insert the key, open the door or turn on another light

There are 3 wires one is negative (ground to chassis (i think)) one seems to be positive, the other seems control the ? (magic).

How would I wire this with my own lights and switch to keep the current functionality?

Looking at the current built-in light/switch:
For ON the all three wires are connected together, which turns on the other internal lights too (activating there magic)


I couldn't see or find a switch that combined three wires in the manor I understand.

Sorry about the vocabulary used, I have a limited knowledge in this area.
 
Solution
I did some tests and rechecking.

1) 0 - 12VDC
2) Ground
3) 1.2VDC (one point two)

1) is either 0V or 13.4V when doors open or another light is switched on
3) when connected to 2, powers 1

rjenkinsgb

Well-Known Member
Most Helpful Member
It's most likely a light fed from battery positive controlled by a switch to chassis (0V).

The third connection is the from junction of the light and switch, to the door switches etc., so any other switch to 0V also turns the light on.

The extra switch position breaks that connection, so the light is not turned on by external grounds.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Actually, the one time I worked with one of these the common wire was always 12 volts, and the always-on position or the door switch connected to battery negative.
That's what I described - Power to lamp, switch to 0V??

It could be replicated using a standard three position on-off-on changeover switch:
Switch common to the non-power side of the lamp, one ON to 0V for forced on and the other ON to the external switch circuit.
So, the switch positions become ON, OFF, AUTO.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
No problem, I was not sure if my explanation was clear, without a diagram.

My knowledge is also from working on cars, but several decades ago; it's possible that newer electronically controlled one may works differently or indirectly via the electronics - eg. if the same switches on the doors are used for door not closed warnings etc.
 

Tony Stewart

Well-Known Member
Most Helpful Member
I believe JCI is one of the biggest designer/suppliers of auto interiors and here are some overhead switches.

My guess is the switch is a simple SPDT with a centre off position. Simulated https://tinyurl.com/2dve3ok5

Beware of fuse ratings and load for your lights are suitable. I think this only switches voltages with the source on the centre wire. So choose the terminal that provides +12V and use the Chassis for 0V.

1666100666291.png
 

TheOtherShiny

New Member
I did some tests and rechecking.

1) 0 - 12VDC
2) Ground
3) 1.2VDC (one point two)

1) is either 0V or 13.4V when doors open or another light is switched on
3) when connected to 2, powers 1
 
Solution

shokjok

Member
The third wire could be from a delay timer, activating the interior light(s) when a door opens. A wiring diagram will identify the timer model and location in the circuit, likely the PDC/ fusebox.
 

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