I have a 12 V relay module, as pictured below (not this exact image, the relay has 12 V logic, not 5 V as in the picture.)
I am getting a voltage reading from the signal, it's floating around 12.2 V all by itself when there is nothing connected to the signal.
The relay works as expected: when signal is connected to a battery the relay switches; disconnect the battery and it goes back to the previous position.
After doing this it will show 0 V on the signal, but leave it for 10 minutes and signal will start to give off a voltage reading again.
The above signal is a 12 V high signal, when a vehicle ignition is turned on it provides a 12 V signal to this relay and a GPS tracker signal input.
The problem is when the ignition is turned off (12 V signal is turned off) the relay goes back to its default position and the GPS tracker turns off as expected.
Give it 10 minutes and the INPUT on the relay module starts to give off a voltage which triggers the input on the GPS module to think the ignition is turned on.
I have tracked everything back to this relay module, everything works fine if this relay module isn't connected, and I have put it on the bench and replicated it using a bench power supply.
My current idea is maybe the input is floating and needs a pull-down circuit added to it, but I would have thought a module like this would have covered this scenario already.