Thanks Joe but I'm happy with the relays, it's the wiring to the loom plugs in which I'm now interested.
If you look closely you'll see a tiny number moulded into the plastic beside each wire connection. Is it possible to check that they are wired as follows:

Connector C0019
Pin 1 = brown thick
Pin 2 = blue/red
Pin 3 = no connection
Pin 4 = yellow

Connector C0088
Pin 1 = blue
Pin 2 = no connection
Pin 3 = no connection
Pin 4 = black thick

Simon

I have this photo from previously

Thanks Joe. That all looks as expected. There's no connection to the incoming medium speed wire and there's no third relay in the control box so I remain puzzled.
Still, the important thing is that you've got the fan working properly without any drastic surgery. Congratulations!

Simon

Thanks, biggest job I’ve done yet, learnt a lot, had no idea what I was doing, just following threads, started off as brushes, then resistors, then relays, thanks for hanging in there with advice!