So lets break this down a bit …
- You don’t need an internal drive to run your system if you use a bootable USB, FireWire or Thunderbolt drive.
- You don’t need the internal keyboard, a USB (preferable) or Bluetooth will do.
- You do need the trackpad, be aware the trackpad has a thermal sensor which is poled by SMC, if not found the system will go into CPU Safe Mode to protect your system from overheating. As such the fans will ramp up and the CPU’s clocking is reduced. Best to plug it in.
- You do need a internal display unit plugged in for the the same reason there are a few sensors within the display and the iSight camera.
- You also need battery if you want to see if the GPU is working. And of course DC-In board and MagSafe charger to run the system.
So unless you have extra parts (trackpad & the correct Internal display & good battery) which you can connect to your logic board it will be tough!
I had a sweet setup to test logic boards back in the day, but I was very focused on a limited number of models so I could spare the hardware to do this. I was fixing about 20 or so 13 & 15” MacBook Pro’s per week for some large companies which had just them.
Fixing a logic board is a very different endeavor! There we use a bench power supply, DVM and a scope to test the raw board when we already have a direction in mind on what needs to be fixed.