Question Troubleshooting ethernet cable

[requiredAlias]

Hope this belongs in "Networking." I have an ethernet cable running from one end of my house to the other (60') through wall outlets. All a single ethernet cable. Runs from my router to a 2nd router set as AP. Has worked perfectly for years. A few days ago it stopped working. The LAN light on the AP is off, indicating no signal from cable. Wireless signal is badly degraded near the AP. I can connect my AP to the ethernet cable that runs from the router to the AP and the LAN light lights up. Thus, I know? THAT cable is good and, as a consequence, the cable running through the walls/crawlspace is the problem.
I've checked both ends of the cable. Both look in good condition. If I have my lingo right, both ends connect to the cable by RJ45 connectors. How can I, if possible, test the connectors and determine how to repair?

 

[helpstar]

connect a different device to the long cable´s end, might still be the AP

 

[bill001g]

You could try something like this. This is just a example it is the first that came up on amazon.
https://www.amazon.com/iMBAPrice-Network-Cable-Tester-Phone/dp/B01M63EMBQ

These will find most the simple cabling problem a home user has.

Unfortunately it only actually tests if a battery can light a led over the wire it does not actually test that the cables can actually pass data signals over them. The meters that can do that cost many hundreds of dollars and many times closer to $1000 if you want to actually certify cables. The other stuff between these price points is junk so there really is no way for a home user to do other than basic tests. It tends to be cheaper to just run new cable than buy expensive meters to test and you might end up doing that anyway.

The good news is the wire itself seldom goes bad after it was working. Maybe a rat chewed on it or you drove a nail though it but they do not just fail by themselves. The end though do get corrosion on them and can break internally where the wire connects to the inside of the pin. Generally you just cut off both end and carefully re terminate them to fix bad cables.

 

[BFG-9000]

The cheap continuity tester will only tell you if both the cable and ends are good (but not which one is bad, though it will at least tell you which wire in the cable is bad), while the tone generator type will actually tell you how far away the rat chewed through the wire so you know where to look for a break (and the cable certification checker tests at high frequency and for crosstalk)

With only one 60' line it's easiest to just inspect the whole length of the cable and replace or splice as needed

 

[requiredAlias]

You could try something like this. This is just a example it is the first that came up on amazon.
https://www.amazon.com/iMBAPrice-Network-Cable-Tester-Phone/dp/B01M63EMBQ

These will find most the simple cabling problem a home user has.

Unfortunately it only actually tests if a battery can light a led over the wire it does not actually test that the cables can actually pass data signals over them. The meters that can do that cost many hundreds of dollars and many times closer to $1000 if you want to actually certify cables. The other stuff between these price points is junk so there really is no way for a home user to do other than basic tests. It tends to be cheaper to just run new cable than buy expensive meters to test and you might end up doing that anyway.

The good news is the wire itself seldom goes bad after it was working. Maybe a rat chewed on it or you drove a nail though it but they do not just fail by themselves. The end though do get corrosion on them and can break internally where the wire connects to the inside of the pin. Generally you just cut off both end and carefully re terminate them to fix bad cables.

Thanks to you and BFG. Sounds like I'll find a contractor to do the crawling under the house and do the troubleshooting.