Thankyou guys, i managed to speak to the guy who did it, i understand what he was trying to do now, the switch was a back up incase the thermostat failed on him again. So it was still wired so that the thermostat could turn the fan on, but also be turned on from the inside of the cab if needed. The fan stopped working when the thermostat went I think. In any case I temporarily wired the fan directly to the switch in the cab avoiding the thermostat all together and have now installed a new thermostat and should be sorting out the rest of the wiring with someone who knows what they are doing this week😂 honestly has been far too dangerous driving around having to remember to switch the fan on. Thankyou for that schematic though, much more usefull in colour 👍 Will post an update when its all sorted