Would there be any harm done?
 

I am restoring a 1988 S4. I purchased the car from a salvage yard, rescued it, not really knowing much about it. I did know the engine had to be worked on, but did not know how bad. I have removed the engine. Opened up the oil pan and the engine is gone with the thrust bearings grounded into the wall of the block. Well I have purchased another engine and now its up on a stand and I am replacing some sensors (knock sensors). My question is that while I am waiting on motor parts would it be harmful to any electronic parts in the car if I put a battery in it and worked on some of the interior items. (seats, lights fan motors, ect. Thanks for your help.

Engine in or out isn't the big factor, any shorts is the big factor. Loose wires that might ground against the chassis, previous damage in the wiring that is shorted out, but otherwise I don't see any problem with putting in a battery and starting to sort some issues out.

Disconnect it while actively messing with the electrics, and maybe disconnect the brains?

make sure you pull th fuel pump relay, you dont want to spray raw fuel every where

Thanks for the information. I am going to start on the inside while the parts are coming in on the motor.