If you’re just starting out doing diagnostics, get the cheapest obd2 reader. $10-20 gets you a bluetooth reader that you can read on your phone. ELM327 (for android, there’s another for iphone)

This will cover 90% of your issues…glow plug definitely. The code will even tell you which glow plug.

Working on sbc brakes…just disconnect the large connector at sbc unit before doing work, and reconnect when done (before you put key in)

Glow plug controller is definitely a pain, but i had that issue only on one car (out of 4).

Mark