Relay and socket harness for 5 or 4 pin standard automotive relay. standard nakid female blade terminals can be crimped to wires and pushed through the block from the top. The blades may need a slight tweaking once pressed in to allow the blade on the relay to fit easily. It may be hard to get it to seal at first but once it conforms to the block it will install and remove easily with the terminals remaining in the block. The design included has a mount bracket that can be used to attatch it to anything. Edit the file if you like and make a custom relay box.
I have tested this with 8% infill and it works decent. The mounting tab is not as strong but it works well.
I have a few 3d print videos if you want to check them out on: https://www.youtube.com/camarorick