Radiator Fan Switch Problems

Hi all, I have read through all the radiator fan threads I could find but none solved my issue:

My radiator fan sometimes just doesn't switch on. After a number of stopping on the side of the road moments and manually bridging the thermoswitch, I have decided to put in an override switch on my dash, thus allowing me to switch on the fan whenever it doesn't want to ( I also hooked it up to an old car alarm light in the dash so I know exactly when it's on).

Strange thing is, after installing the switch earlier today, I ran the car hot and the fan switched on by itself. Then I ran it hot a second time and this time the fan didn't switch on. I then switched my override switch on and off and presto the fan is now running on its own again. Now I would see this is a broken/ stuck relay, however it seems that the fan's circuit doesn't have a relay in it, or am I mistaken?

Anyone have any advice as to what I should replace or check?

Thanks  

all it has is live feed to thermoswitch, then a wire from there to fan plus an earth from fan to battery/lighting loom.

to check fan and wiring unplug the thermoswitch wires and bridge them together. if fan comes on each and every time no problem, replace the thermoswitch. if not check the wiring.

to check fan jump it straight from the battery, if its still ropey replace the fan