'88 300SE Aux fan resistor location

Can anyone please tell me where the aux fan resistor is located on my 300SE - I have a new one but can't for the life of me find where it goes! The fuse for the aux fan keeps blowing and the car idles hot (temp is normal during driving). I have replaced the thermostat and the aux fan. After the resistor next up is the fan and clutch - any help would be greatly appreciated as I am a bit wet behind the ears when it comes to working on my new/old Mercedes.