Cable tester is typcally two-part: handset and a dongle on the end of the cable. It will tell you whether you made a mistake in wiring, a distance where a wire is broken, so you know whether you need to replace the entire cable or just a single plug. Without tester finding a fault is a matter of try and error, but plugs are cheap, hope you bought it in excess.After all that hard work inside the roof, the furthest AP, connected with a store bought 30m cable, connects at 100Mbps FDX and not gigabit.
AAAAARRRGH! This is a lesson, test the cables before you use them. In my case, will borrow a tester to see which pair is faulty , hoping all I need to do is just re crimp new jack's to get back to gigabit.
If the cablee is layed improperly, speed will also downgrade. Observe 10cm radius, no sharp corners or an unneccessary tension.
Coverage? Do you really connect this AP by Ethernet cable or a wireless (mesh type)? The later would explain your question.