I would like to run it through the switched power. So off when the truck is off
Just one button to turn off the mirror lights
I am really not too concerned about driver tampering. But I would like to be able to make it look OEM.
I love your idea of tapping into the existing door switch. You kind of lost me in the way the unit could be built. I would love to find some existing unit for cross application.
I really appreciate the help!
Clint
It's doubtful you will find 'an existing unit' that you can use without a lot of modification.
The door switch in most automotive applications is a normally closed switch that is 'held' open when the door is closed. When the door opens, the switch returns to it's normal position and closes.
So, if you want to use the existing switch, use a multi-meter and ensure there is 12V on the wire (usually one) that goes to the switch when the switch is depressed. When you release the switch, it connects that wire to ground completing a circuit and you will measure 0V on the wire.
If this is the case, you simply need:
- any 12V relay with 'Normally Open' contacts. (Which is pretty much most of what you will see)
- a Diode
- a normally Closed Momentary Button. (Which will be the 'off' button for the driver to turn off the check mirror indicator)
- an indicator. (Which you can make anything you want. Light, Buzzer, squirt gun, etc.)
The wiring may catch you a little off guard immediately, but what ends up happening is that a relay has two halves.
An input side, and an output side.
The input side is two pins that will activate the other side when you attach power to it.
The output side is 2 or more pins that will either internally connect to each other, or disconnect from each other when the input side gets power.
They are almost always used to trigger something big with something little, because a little AA battery can trigger a relay to activate, and the relay can handle things like a starter or high power lights. We will be messing with that a little. We are going to make the relay trigger itself.
Wiring is quite easy, once you realize you only need to connect two of the relays pins together to make it work.
So, switched power goes to the relay. (Pin 1)
You can use a tap-in on the door switch in the truck. You will connect the relay (Pin 2) to this wire with a diode. (This is to allow the door to activate your circuit, but to disallow your circuit from activating the door)
Now, you build your indicator, and connect it to switched power, but instead of connecting it to ground, you will connect it to the relay. (Pin 3)
Then, you connect the relay to ground (Pin 4)
At this point you have a working 'momentary' indicator. When the door opens, it completes the circuit for power to flow across pins 1 and 2 (The input side)
This then connects pins 3 and 4 together, and considering your indicator is waiting for pin 3 to connect to ground, your indicator now turns on.
To make this 'latch' we have another step.
Connect the Normally Closed button to pins 2 and 3... This switch will end up powering the relay by itself.
Remember that the Door Switch connects to ground when the door opens. This allows power to flow from pin 2 to ground. which triggers pin 3 to connect to ground, which is also connected to ground! So now the door closes, and pin 2 is no longer connected to the ground through the Door switch, but it's still connected to ground through pin 3 because it was activated! It now latches
To turn it off, when the button is pressed, it disconnects pin 2 from pin 3. Which means that pin 2 is not grounded anymore and the relay turns off. (As does your indicator)
You can also turn the key off in the truck. It won't matter if pin 2 is grounded if there is no power. The relay will turn off and the door will need to be opened to trigger your indicator again.
*There is a flaw in this design though. If the door is closed before the power is switched on, the indicator will not light.
**If you have issues imagining the the wiring, I can try to draw a picture.
