Before installing the new Solenoid, pour some clean engine oil on it! You do this to protect the O-Ring seal from damage when you fit the part!

To replace the solenoid, connect it to the wiring harness, then you are going to lie on your back under the wheel arch so you can see the hole it goes in. Holding the body, you reach up with it, and very carefully locate in its hole and push it in! Leave it out a little, the distance between the o-ring and the body.

You can now use your extensions to place the screw through the Solenoid's mounting hole, align it with the hole in the engine and slowly screw it tight!