One important thing to know is hat USB C cables contain 4 pairs of high speed signals, (TX1, TX2, RX1, RX2) and only 2 pair is used for USB 3.0. You either need to use TX1 and RX1, or TX2 and RX2.
Just connecting the signals to the other outlet does not work, you don't know if both sides have the cable in the same orientation.
This requires you to do cable orientation on both USB C plugs and switch your mux to the proper pairs
According to table 3-10 in the USB C spec:
| USB Type-C Plug #1 |
|
Wire |
|
USB Type-C Plug #2 |
|
| Pin Signal |
Signal Name |
Wire number |
Signal name |
Pin Signal |
Signal Name |
| A1, B1, A12, B12 |
GND |
1 [16] |
GND_PWRrt1 [GND_PWRrt2] |
A1, B1, A12, B12 |
GND |
| A4, B4, A9, B9 |
VBUS |
2 [17] |
PWR_VBUS1 [PWR_VB US2] |
A4, B4, A9, B9 |
VBUS |
| A5 |
CC |
3 |
CC |
A5 |
CC |
| B5 |
VCONN |
18 |
PWR_VCONN (See Section 4.9) |
B5 |
VCONN |
| A6 |
Dp1 |
4 |
UTP_Dp |
A6 |
Dp1 |
| A7 |
Dn1 |
5 |
UTP_Dn |
A7 |
Dn1 |
| A2 |
TXp1 |
6 |
SDPp1 |
B11 |
RXp1 |
| A3 |
TXn1 |
7 |
SDPn1 |
B10 |
RXn1 |
| B11 |
RXp1 |
8 |
SDPp2 |
A2 |
TXp1 |
| B10 |
RXn1 |
9 |
SDPn2 |
A3 |
TXn1 |
| B2 |
TXp2 |
10 |
SDPp3 |
A11 |
RXp2 |
| B3 |
TXn2 |
11 |
SDPn3 |
A10 |
RXn2 |
| A11 |
RXp2 |
12 |
SDPp4 |
B2 |
TXp2 |
| A10 |
RXn2 |
13 |
SDPn4 |
B3 |
TXn2 |
| A8 |
SBU1 |
14 |
SBU_A |
B8 |
SBU2 |
This shows that the cable swaps the signals around, every side transmits on the A2,A3,B2,B3 pins, and receives data on the A10,A11,B10,B11
You would need to take the data in from pins A10,A11,B10,B11, feed to though a mux, then another mux for the other port and then send it out on A2,A3,B2,B3 for both directions.
Depending on your exact muxes, you might need a active repeater in between to make sure the signals stay outside the eye
Connect shield to the body of the connector. That's literally what the shield is in such a cable.
If it's not exposed on the breakoutboard, you may be able to solder it to the shroud of the connector. Note that this is a bit risky, as you may melt the plastics if not careful.
If it's not exposed and you don't want to solder, you will probably be fine without shielding. The keyboard uses USB1, which has far lower bandwidth than USB2/3, so it will probably work fine without shield connected at both ends. It's unlikely to break anything.
Best Answer
The drawing seems to contain the number you want:
You're lucky- quite a few USB-C receptacles I've seen don't specify this, so you just have to eyeball it (perhaps why so many connectors you've seen stick out a bit)