This is a remastering of the once popular Crazy Contraptions / Part Randomizer mod by @umustbeloggedintododat (I got his permission to do so) that unfortunately broke for a while. I have now revived the mod and will be adding new features to the mod. 
Crazy Contraptions RemasteredUI App
Instructions
- Add the Crazy Contraptions Remastered UI app to the UI layout
- Press one of the buttons
- Wait a little for the magic to happen
Note: It will only randomize parts of the chosen vehicle and doesn't also randomly pick a new vehicle.
New Features
- No more spawning with incompatible parts (e.g. diesel engine will spawn with a diesel fuel tank and will not spawn with a battery or gasoline fuel tank)
- Now can scramble tuning values and paint colors!
- Front and rear diffs will choose same final drive ratios, preventing drivetrain/gear windup
- Now can randomize body parts and drivetrain parts solely
- Body parts can be empty now
- Toggle scrambling with "empty" part
If the mod isn't working for you, try pressing Ctrl + L to restart Lua. And if that doesn't work try disabling all other mods and restart Lua, because you may have broken mod(s).
Credits: @umustbeloggedintododat for the original project @N_S for the scramble paint code and reporting bugs