This morning my 05 700 carb would not crank, dead battery. Hooked my batt charger up and the cooling fan came on, even with the ignition switch off. Need help, have no idea what's wrong.

 

Sounds like the temperature sending unit (either on the cylinder or radiator, can't remember) has failed. That sender is supposed to complete the circuit to the fan ONLY when at a pre-set temperature.

If you unplug the wire from the sender, the fan will stop.

Remove & test to be sure, & replace.

 

I think i have read somewhere that it is the senser for it to come on is bad.

 

Unhooked the sensor next to the thermostat housing and the fan still runs all the time.

 

Sounds like your ECM went bad. They hace a recall on them. RECALL

 

Disconnected the batt cables and charged the batt. Now whan I hook the cables back up everything is fine. Starts OK and fan does not run all the time.

 

Yeah thats the way my buddies 05 700 did.

 

Electrical problems can exhibit strange symptoms sometimes. As long as your charging system is keeping the battery fully charged, you might be all set.

 

It worked ok for about 15 min. Then the hot light started flashing and the fan wouldn't shut off again, even with the switch off. How much does an ECU cost and where is the best place to buy one?

 

Your machine shouldn't even have an ECU. You don't have fuel injection. Even if you did, that is a last resort if all else fails. They are NOT cheap.

Sounds like you have some other issues going on. Is your coolant level where it should be? Any leaks? Radiator plugged with mud?

If the sending unit senses high heat, it will run wether or not the key is on.

You need to find out why the machine is overheating first, if it is overheating. Did you plug that sensor back in? There are 2 sensors on my machine, but mine is fuel injected (needs a temp. sensor for the ECU to determine fuel mixture). Usually, the sensor is located in the back of the radiator on one of the sides.