Use old Airport Base Station as External Hard Drive

When I plug the cable into the WAN-O port of the base station and an outgoing Ethernet port on my router, in my Network, I get something that says "Thunderbolt Bridge" which is not connected (red dot) and can't do anything with it.

I am not able to duplicate the error that you are reporting. "Thunderbolt" would only appear if you are trying to use a USB cable or USB to Ethernet adapter, which you do not want to do. You need to use a regular Ethernet cable. It will look like this on both ends of the cable and the Ethernet ports on the router and Time Capsule will look like the second example below:

Double check this before you proceed any further.

Next, let's make sure that the Time Capsule is connected to your router correctly.....and....configured to work on your network. When this occurs, the Time Capsule will be set up automatically in Bridge Mode, so you don't have to worry about this.

Connect an Ethernet cable from one of the LAN <--> Ethernet ports on your Wi-Fi router to the "O" port on the Time Capsule. Most Wi-Fi routers have 3 or 4 Ethernet ports, which are labeled <-->. Use any one that you want.

Power up the Time Capsule and let it run for a few minutes

Then, hold in the reset button on the back of the Time Capsule for 7-8 seconds and release

Allow a full minute for the Time Capsule to restart and display a slow blinking amber light status

Open AirPort Utility on your Mac

Click on the Other WiFi Devices button in the upper left side of the AirPort Utility

Click on Time Capsule xxxxxxx

When you click on Time Capsule xxxxx, this will start up the AirPort Utility setup wizard which will display the correct window to configure the Time Capsule, which will look similar to the window below except that you will see a picture of the Time Capsule.

Network Name......Type in a short name for a Wi-Fi network (you won't use this network, but it must be set up)

Base Station Name....Type in a device name that you want to call the Time Capsule

Password.....Type in a password

Verify.....Type in the same password again

Click Update and give the Time Capsule a minute to restart and display a green light. When the green light appears, the Time Capsule has been set up correctly to connect to your Wi-Fi router's network....and...the Time Capsule has been set up automatically in Bridge Mode.

Post back on your progress and we will continue.

You would use Migration Assistant on the Mac to transfer data from a Time Machine backup over to the Mac. The support article mentions a "new" Mac, but that is really the same as an "older" Mac

Restore your Mac from a backup - Apple Support

It won't be cheap, but you could take the Time Capsule and your Mac to a data restoration specialist to have them show you what files would be available from the Time Machine backups to transfer to a folder on your Mac.

Good luck!

Apple assumes that you will be transferring files from a Time Machine backup over to another Mac to make the "new" Mac look like the "old" Mac.

Now if you are using the same Mac that made the backups, you should be able to use Time Machine normally to go back and pick up the files that you want.

There are other methods to transfer data, but they are not supported by Apple, so the forum moderators will pull that information if we post on on this site.

I did not say that. I said that there are other methods, but they are not supported by Apple.

If we provide the complicated details, and one of the Apple forum moderators sees the info, they will delete it based on past experience.

If we provide the complicated details and it makes it past the guards, we cannot provide any guarantees that the method that I have used in the past will work for you now on your network.

Try Googling around....something like "transfer files from Time Machine to a Mac without using Migration Assistant".