Recently I have noticed that the main fan on the radiator is not turning on. When I’m in traffic (say less than 20km/h) the temp creeps up and as soon as the car starts moving goes down. When I turned the air con, only the smaller fan turns on.

My question is how do I determine if the main fan (closer to the battery) is working correctly?

My understanding is that is could be one of 3 relays in the fuse box, actual fan, dodgey connection somewhere? Anything else? And where do I put the voltmeter to check the voltage in the circuit?

Was pouring rain last night so I didn’t get a chance to take a detailed look at it…. Except that the fan is not turning on with air con.

Have a look in the workshop manual as there is detailed data on testing the fan and each of the 3 relays. There also should be a bit on testing the coolant temp sensor which tells the ECU to turn the fan on.
Not sure if this test works with Magnas but does on other Australian made cars and tests the sensor: switch ignition on, remove connector from coolant temp sensor, after 10 seconds (or so) the fan will switch to LO, then a bit later it will switch to HI.
Here is the link to the manual: http://www.lisho.net/?page_id=3

can you elaborate in terms of where the voltometer needs to go?

can you elaborate in terms of where the voltometer needs to go?

I'm pretty sure you measure the volts etc by removing the relay - the multimeter prongs go in the slots where the prongs on the relay normally goes. (they should be numbered) The manual tells you what hole and what you should expect to see on the meter etc.