Switch 12V with 3V control circuit
If you have 4 volts on the emitter then you must also have 4 volts on your &quot;always ON 12 volt&quot; line. If in fact you mean &quot;collector&quot; then fix your question.

You are completely right! Facepalm moment! I mixed up collector and
emitter. I need to check what way I connected it on the lab deck. I'll
be home within the hour. Will be updating the question. Thank you!


Yep, it was the transistors mounted the wrong way. Now it works fine.
Thank you again. Sometimes all a problem needs is a fresh set of eyes.

A little bit of interrogation usually sorts many problems out. Good luck.
BJTs are a bit bi-directional (they are NPN or PNP for example) and, can be swapped around (with care) but one of the drawbacks is that current gain is greatly reduced and this is the likely problem.