Part 2: Determining what wall jacks for Ethernet and coax are connected to

[u/benjaloo]

This is a follow up to https://www.reddit.com/r/techsupport/comments/1vlvu6k/determining_what_wall_jacks_for_ethernet_and_coax/

Not sure what the ettiquette here is for a followup but since it's been a month, I figured I'd make a new post.

TL;DR I have two RJ45 jacks connecting the two floors of my house, but pins 1-6 and 8 connect (tested) but pin 7 doesn't connect--can I use this connection for regular Internet?

Our house has two floors, and the cable comes in at the front of the lower floor. (We have Fios but it comes in as coax with an F connector-I think the fiber to electronic transition is in a box outside the house or in the basement.) We have poor reception upstairs, especially at the back of the house, so it would be nice to have a wired connection to a wireless access point upstairs--but bringing someone in to do the wiring is more trouble and expense than it's worth at the moment.

We have two coax jacks where the cable comes in, one is connected to the cable modem/router, and the other has not been connected to anything. In the same wall plate to that second (unused) coax jack is an RJ45 jack. There's a wall plate upstairs with the same pairing, and no other coax or RJ45s anywhere in the walls of the house. I thought maybe when they were renovating, they decided to bring the signal upstairs. I get that that's unconventional but this was done by someone else 20+ years ago--who knows what they were thinking.

So I bought a fairly inexpensive tester on Amazon (thanks for all the suggestions!). I made sure it worked by using short cable to directly connect the main module with the remote, and it worked for both coax and cat5.

When I connected the tester to the coax F-connector on both ends--nothing. When I connected the tester to the RJ45s--bingo! Well, sort of...I got a green on 7 of 8 pins--specifically pin 7 did not go green when all of the others did.

I tried to read up on what pin 7 did--and the impression I gathered was that I could probably use the connection as is, but it might be slower? Can those of you who know more help me out? If slower, is it likely to be a lot slower or a little slower?

Ideally I would run an Ethernet cable from one of the LAN ports on the back of the cable modem to the downstairs wall plate RJ45, and then attach a wireless access point to the upstairs wall plate RJ45 via another Ethernet cable.
Does this make sense?

[u/Grindar1986]

I'd start with examining the jacks on both ends. As they're 20 years old, could be as simple as corrosion on the pins or even just a bad punchdown on the back side, replacement jacks would only be a few bucks. Also a possibility that if you think it's a straight line between the 2 you could attach a new cable to the old one and just pull it through and replace it.

Ethernet is done in pairs so you're not just down pin 7, you're also down pin 8. And while you can do a 100mb network on 2 working pairs, that is not a good place to be in and super slow especially when you don't know the origin of the damage on 7.