Heater Control unit testing

[Jellybean]

Hi

 

Going to try and diagnose the issue ; any help appreciated , I have a few youtube videos to look at on how to verify transistors are working

 

So far

 

• I need to test the car loom again as it has two 12V feeds not just one, Illumination and HVAC
  
• Look for visibly cracked solder joints
  
• The most likely ones are the transistors TR1 & TR2 and the Zener diode ZD1
  

 

Any other suggestions ? wheres Heckler when you need him