Relay only lights up LED, but does not click or switch. Help is appreciated!

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Hi, so I am building a camera slider using an Arduino Mega with RAMPS 1.4. 99% of the circuit works. The only trouble I have left is that my camera shutter Relay does not click. It only lights up the LED.

The relay has + - and Signal.- Signal is connected to the Arduino and the + and - go to a 5V power supply. That power supply is then connected in paralel to a 12V car batttery alongside the Arduino itself. I also have two stepper motors and a huge display connected. That stuff all works fine.

When the Arduino is runnig it only lights up the LED when it is time to take a picture, but the Relay does not click. I checked the pins on the relay and there is 5.6V across it from the power supply. So it does get a signal and it has power, but still no click.

If I short Signal to +, it does click, but it doesn´t click when the Arduino activates it.

What am I doing wrong here?

Usually this is current related.
Is your voltage converter up to the task in that aspect ?

Also there should be a common ground back to the Arduino.
I would run an extra wire from the negative side of that small adaptor back to ground on the Arduino itself first to see if that is the cause.

Measure the current into the relay input pin, when connected to +, and the voltage between Arduino Gnd and relay - (should be zero, but…)
Measure the voltage on the relay input pin, when controlled by the Arduino.

Please share circuit diagram

And your code (post using code tags...)