Bathroom light pull switch wiring with secondary pull switch

Hi, I have a pull switch at the bathroom door which does two things
1. Turns on the ceiling light
2. Powers another pull switch next to the shower cubicle which allows a light in the shower to be turned on and off.

So, if the main bathroom light is off, then the shower pull switch is off. If the main bathroom light is on, then the shower light can be put on or off with the second pull switch.

The problem - I am replacing the main pull switch and did'nt make a careful note of how it was wired (v. stupid). There are two grey, three core wires feeding into the switch. One of the three core wires had the black wire cut and sealed off.
The earth connections are obvious, but how do I wire the remaining, one black and two red wires?? - Any help will be gratefully received.

there are only two options, i should go for this.

put the sinlge red with the black into one terminal, and the other red in the other terminal

Thank you for the quick reply and the advice - your solution worked first time and didn't blow a fuse.
This is a great site for part time DIYers.