atv cooling fan

I have a 2005 polaris sportsmen 450 and i want to hook up a relay and toggle switch to control the coolant fan . but I don"t want it to back feed into the on board computer and if I disconnect the wire going to the fan the Hot light on the dash with stay on . but I would like the computer to still operate the fan as well . its a !2v system and the fan draws 40 amps . I was thinking a inline diode but not sure were to install it or if they make one to handle 40 amps . thank you

The fan should use a relay, hence you should only need a IN4004 (1A) or similar diode if using the same relay. If the fan is hot (always +12V) with the relay in the ground circuit, then a parallel relay can be added without effecting the existing circuit. The same can be done if the relay switches the +12V to the fan provided the same +12V source is used for the second relay. The above assume no fancy sensing of fan current, but fan circuits still seem to be basic - on-off lamps are usually taken from the relay trigger circuit (ie, from #85 or #86) - BUT I have no knowledge of the 2005 polaris sportsmen 450 circuit & wiring.