Hello, I have a switch that I am using on my truck. The switch is being used to complete a 5 volt circuit. I want to add an L.E.D. light that mounts in the dash to turn on when the switch is on. Is it possible to use the 5 volt wire to the relay to turn on the 12 volt L.E.D.? If so, could someone please explain how to wire it and a diagram would be great. Thanks!
If it will light up a 12 volt LED it will be very dim. Why not get a standard LED and wire a 100 ohm resistor in series with the LED.
Because there is a certain LED that I am planning on using. That's why I'm asking, isn't there a way to run a 12 volt wire into the relay so that when the relay senses the 5 volts from the switch it connects power from the 12 volt line to the light, and giving the light the full 12 volts? The only thing the 5 volt line would be used for was to signal the relay to close the circuit from 12 volt constant to the light.
You could do it with a standard 12vdc automotive relay:
Rewire your current switch so that one side is grounded and the other side goes to pin 85 of a Bosch style relay. Wire Pin 86 to constant (or ignition) 12vdc
Use the contacts (Pin 30 = Com, Pin 87A = NC, Pin 87 = NO) to complete your 5vdc circuit.
You can then connect the (-) side of your LED to Pin 85 of the Bosch relay. Wire the + side of the LED to 12vdc constant or ignition.
You will also need a diode across the coil of the relay - connect the striped side of the diode to Pin 86 and connect the "unstriped" side to Pin 85. This diode will protect the discreet LED from being damaged from the collapsing of the magnetic field in the relay coil when power is removed.
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Kevin Pierson
Thanks for the replies, I got this suggestion from someone else...
I'm sure you won't understand the wording but the wire going to the air pressure sensor is the 5 volt circuit. The resistor is to prevent a CEL from being thrown.
