Draw Lines on Surface without editing the Surface

Hello

I am making a plan for a renovation of our house.
I like to draw on the Walls where the Wires shall go between the Lights, Switches and Plug Sockets.
Also I like to draw where the Tubing for the heat radiators shall go.

How can I draw lines one an Object without actually changing the Models surface?
Also Is it possible to change the color of these Lines?

Thank you.

Make the walls a group or component before drawing the lights, switches, and receptacles.

You can apply materials to edges and then set the edge style to By Material in the Styles Edit window.

@martin78, and preferably lock that group before drawing on/over its faces. Otherwise at some point you may inadvertently move the group.

@DaveR @Wo3Dan
Thank you for your Tips. I will try to do that.

Guess I did something wrong in a Step before that.
First I had build up the entire Floorplan of the 2nd Floor.
Then I started to Design the Bathroom. The rest of the Floor was in the Way So I selected only the Bathroom Walls and Floor, cut it and paste it in a new Layer.
But now the rest of the Floor is still showing up in the new Component / Group I created. Also reacts to what I draw.

Will read the manual / tutorials about Groups and Components soon.

Before you do anything else, go to the help files and read about layers in SketchUp.

Layers do not provide separation between edges and faces. Only groups, components, or actual space can keep things separated. Layers only control visibility.

Layer 0 should always be left as active. All edges and faces should remain on Layer 0. You only make layer assignments to groups and components.

Allright - I got it.

Layers do not Separate models but just visibility.
So work with groups or components instead of Layers…

When I build everything in Layer 0
Is there a quick way in to hide everything else but the selected group or component?
For altering details of the group without getting the view blocked by other groups or components.

Yes. And then make a group or component and give it a layer assignment if you wish. The edges and faces inside the group/component stay on Layer 0, though.

You can turn off the other layers by unticking their visibility box. If you want the others to temporarily disappear while editing a group or component, go to Window>Model Info>Components and tick the boxes for Hide Similar and Hide Rest of Model. this works well unless you need the other parts of the model for reference. Setting the Face Style to X-ray may be useful instead.