Serial Input reading question

I am trying to read a serial input and see the results on the Arduino’s built-in monitor.
This is to verify I am reading the data before I process it further.
My problem is eiter one of physical connections, or code or both.
The data coming in terminates in a USB plug and consists of numbers…eg 0254,0223
A different number is received every few seconds.
I can plug this USB plug directly into a PCs USB port and read it using a dumb terminal (puttytel).
So I would like to see the same on the Arduino’s serial monitor just to prove the data is going into the Arduino before I write code to do maths on the numbers, but I cant.
Either my simple code to forward the data in, to the USB link between the Arduino and PC, or my physical connections to the Arduino from the data’s USB plug are wrong.
I have gotten a USB socket on a cable and soldered the four wires to 22 swg single core wires. I’m not using the power (+5v) wire. So I have the other three D+, D- and Gnd. Gnd wire I presume goes to a ground pin on the board. Where do I plug in the other two?. I have tried all the digital pins, and I have tried a lot of code to try and read it, a lot of simple sketches with no luck.
Any help please?

https://www.arduino.cc/en/Reference/Serial

Yes thanks for that link. I have come across it and have connected my D- and D+ to pins 0 and 1 (and both ways round) and tried the simple serial sketches, but with no luck. They all seem to read switches that are either on or off. I've tried the functions serial.read and serial.available. Any further help?

D+ & D- from a USB cable are not readable like that. You should connect the cable to a part like FTDI Basic which will turn the signal into 0/5V signal that can be received at the Rx pin (same as the 16U2 does on a Uno).

yes, now we are getting somewhere Crossroads. Thanks for that pointer. Now a bit more info before I go and get one. The data is coming from a unit which has a 6 pin socket. A lead is plugged into this and at the other end is a USB plug, but in the lead before the USB plug is a chip, so I am wondering if my data could be obtained from the socket direct and not from this USB plug. I have no idea what format the data is coming out on these 6 pins. I was wondering if they were analog and could be connected directly to the A0 - A5 pins. Didn't want to try unless I was sure, unless the board cannot be harmed. The unit the data is coming from is powered by a 3v battery, so I don't think there is any higher voltages in play on this socket.

Can you read the chip number, and if so, what the pins the socket connects to on it? Use a meter & buzz it out.

Ah, no. They have molded the chip inside the 'larger than normal' USB plug. Crafty bleaters ! Looking at the FTDI, Official FTDI 5V Arduino Basic Breakout USB - TTL Converter Module for MWC MultiWii Lite at £3 odd what pins does it plug into on the Arduino ..the pins seem to be labelled DTR, RXD, TXD, 5v, CTS and Gnd.