Cat Fan Switch Wiring

So I was tracing an issue with a 5Ek that had the fan running constantly and I found that the issue is with the wiring going to the fan solenoid. For some reason with the fan overide switch in the auto position it has constant power on both wires that come from the ecm. Doesn't seem like it would be posible for the one wire to be shorting out from ground without throwing a code could it?

I don't know how it could be possible for the wires to both have power when they come from the ecm anyways....

 

The two wires that run from the fan solenoid to the ecm are ran wrapped in the stuff cat uses on the rest of the wiring harness. I've traced them back to the ecm and theres no evidence of anything rubbing through it. Unless of course the two wires rubbed through together inside of there.

Only way to test that without cutting it off would be to test the pins on the plug of the ecm.

Anyone have a diagram for the engine harness from the ecm on the 40 pin ecms?

 

Yes your correct. Its a Western Star and it is disengaged by power.

I found a wiring diagram from the ecm plug for the engine harness and its not showing any outputs for the fan (multi-function 4). On the diagram I have for the oem harness it shows all the inputs and outputs for the multi function wiring there but not on the engine side

 

Any one have any idea why there is like a resistor or something of the sort on the one wiring from the ecm to the fan solenoid?

 

Found the problem. Diode in the harness about 6 inches down from the ends that go on the solenoid was gone and causing a short. Don't know why they just didn't use a fuse....