I built the simplex when they first came out, so I can't remember the details, but I didn't have any trouble getting the fan to work. Unfortunately, when gluing some extra lead under the bonnet, I got some super glue on the fan gearbox which put paid to that.
The driver I think was a wagon driver from Duncan's Models. I had to chop his left arm off, but it isn't really noticeable, it looks like he is fiddling with something on the engine.