Automotive electrical question - time delay relay for closed loop

[Gabe]

I want to wire in a time delay relay into a closed loop circuit for a sensor in my car, essentially I only want the sensor to work when a signal is received (from the ignition in this case) operate for 30 seconds and then shut off.

I have the time delay relay, but believe I need a second device to close the circuit. I am not sure what the best device is to use for this. Can someone assist?

[Frankie]

Just wire the relay NO in-line with the signal return from your sensor.

Wire the delay relay trigger to your switched source and you're good.
Many of them can be configured for delay on, delay off, etc.

[Gabe]

Just wire the relay NO in-line with the signal return from your sensor.

Wire the delay relay trigger to your switched source and you're good.
Many of them can be configured for delay on, delay off, etc.

So no ground back to the ECM is okay?

[Gabe]

I grabbed some timers from here

https://www.youtube.com/channel/UCbpu3gvLfIKE2aaYHqsxm0A

thanks for the link, already picked up the time delay relay though

[Frankie]

So no ground back to the ECM is okay?

No, that would be bad.
Just from the single sensor you want to disconnect.
Depending on what sensor you are talking about it will be 2 or 3 wires. 2 wire is usually ground and signal. 3 wire will be power, ground and signal.
The wire sending the signal back to the ECU is the one I would disconnect.