Old satchwell thermostat.

[ianmcd]

Do you have a grey wiring centre with relays in it by any chance ?

 

[Kmass]

What is that single red wire connected to the fourth terminal?.

 

[jeff the gasman]

Ffs. If you can’t work it out on site no amount of comments will help.
Not with this type of query.
Even Sparky’s struggle sometimes.