Wiring fan switch?

[NMcC]

I have a 325i Sport and it never over heats etc, and there has been a brand new rad and viscous fan fitted recently but i was thinking about wiring the fan direct to a switch inside the car as i heard that they are prone to overheating if for example stuck in a traffic jam on a warm day whilst driving at a stop start pace

Would it be worth while or would the wiring of a switch be beneficial? if so is it a big job?

[jmc330i]

You can't operate the viscous fan by a switch, it's not an electric fan.
When the car is moving, the fan blades spend most of the time doing nothing as the airflow through the rad is enough to keep things at the right temp, but when the heat from the radiator increases (when at a stop in traffic for example), the viscous coupling locks up causing the fan to spin at engine speed which then pulls cool air through the rad to cool it.

As long as the cooling system is in good condition and working as it should, there should be no overheating issues at all.

[Brianmoooore]

Who told you that? E30s are not remotely susceptible to overheating in a traffic jam or at any other time, providing the cooling system is all in good working order.
The only reason to fit an electric fan is if you have fitted a non standard engine that leaves little room for a fan between the engine and rad.