Electronics
If your going to do any sort of hardware troubleshooting you'll be dealing with electronics,
What you need, as in if you don't have these, don't start a project:
- Multimeter that supports voltage, ammerage, resistance and continuity tests.
- Various test leads, both probes and aligator clips
- Hot Glue gun- its a perfect way to TEMPORARILY attach electornics while your working on them
- Breadboard for prototyping
Optional:
- Multimeter which supports mreasuring capacitors
- Heat shrink tubing
- Various resistors (you can get 'developer packs' of resistors in the most common ranges quite cheaply)
- Various LEDs
- Automotive relays
- Solid state relays
- Tinkercad or other hardware virtualization account/software