G'day all, I came out to my car this morning-2003 TJ Magna to find a dead battery, I opend the bonnet and found "one" thermo fan still spinning, just though I could stop it by hand then let it go and it would start to spin again but just, The other fan was not moving at all, It must have drained all power from the battery as it was not moving a few hours latter as I had to leave it as I was now late for work.
So any ideas guys as electrics and I dont get on ???

The temp switch, possibly. If I had to guess, that

Can't be as ecu controls relay for fan, usually is a fused relay

But if the ECU is getting told to operate the fan from a dodge sensor, is it not possible that the sensor could still be the fault, or are you saying that the ECU recognizes that the engine is off, along with the ignition, and is no longer reading the sensor?

So I am thinking that I should replace the temp sensor and at under $10 a good starting point, as i unpluged the "suspect" thermo fan and installed the battery and turned the ignition on the other fan did not move till I ran the motor, so am I correct in thinking that they run off their own temp sensor, and if so are they at the bottom of the radiator? and while I am at the Mitsubishi I may as well as replace the relays. Has anyone replaced the temp sensors and is it as straight foward as I am thinking?

Temp sensor screws into the housing near thermostat doesn't it.? If that's the one they just unplug and unscrew. I can't see it being a $10 part. It's the same sensor in my 02 Pajero and I priced one of them with mits 4 months ago and it was $156. I'm assuming for $10 you are getting a second hand one.?

Also I wouldn't say its the sensor as that will effect the temp guage too. I would start with the relay. Rather common for a relay to fail and thus the fan stayed on and flattened the battery. I had this happen many years ago with my VT and quick fix was pull relay out when you get out of the car to save the battery. I couldn't look at it for two days so that was my temp fix. Is your relay working ok.? Have you tested it.?

Ok I may have read things wrong, I thought this was the part that I should be replacing but I shall do as you suggest and start with the relays.
Cheers for the help..
http://www.ebay.com.au/itm/Mitsubishi-Magna-TH-TJ-TJ-Series-II-V6-3-5L-Coolant-Temperature-Sensors-/330847875617?pt=AU_Car_Parts_Accessories&hash=item4d0811f221

Yeah that's aftermarket and not a Mits part. That's what you expect a small sensor to cost, not what Mits want. Yeah start with the basics. I'm not sure if any other relays but if they you can swap them over. If not find someone that can lend you one for a few mins and see if that works.

A quick look at the circuit diagrams shows that the ecu has no power once the key is turned off. So with the key off it wouldn't make any difference if the coolant was hot enough for the ecu to start a fan, because it can't do anything with no power. The coil for the relay is also supplied from the ignition switch as well.

I has to be a fused relay, they always have power direct from the battery.
Try swapping the relays around and seeing if the problem moves from one fan to the other.