1997 pete 379 engine fan won’t cut in for engine temp

I have a 1998 pete 379 c12 (9ns).
For the longest time my engine fan wouldn’t come on when my coolant temperature got high so I just used the manual dash switch. Never fixed this issue. Problem 1

Problem 2 my engine fan now stays on constantly with engine fan dash switch off, my fan air solenoid is constantly getting power when key switched on.

A wiring diagram would be great.

 

the first three posts on the Mechanics page, has listings for Cat, Cummins and Detroit wiring diagrams. Check for it there. If it's not, ask pushbroom to kindly look it up.

 

Sounds like a bad sensor

Weird that it would flip from being constantly open to constantly closed

 

I think the 3406e 40 pin diagram is the same as c12, so I’m working off that to trace the system. I’ve changed the temp sensor and still had the same problem. I think the relay lost its ground, but I’m gonna start from the bottom up and hopefully report back with some findings.

 

Just FYI, I'm not sure about the c-12, but a C-15 doesn't kick fan on until 217 degrees

 

Jump the a/c high pressure switch. Usually switch or the a/c circuit. If you can get it on a laptop it should tell you what is turning the fan on

 

Check the ac switch it can cause that

 

So we finally found the cause of constant engine fan. Wire 226 out of the manual fan switch to the fan air solenoid had constant power When it shouldn’t have. There are 2 wires labeled 226 that come out of the manual switch one runs to the air solenoid and the other I’m guessing was a open jumper to nothing, but it looks like it somehow “plugged” into another open jumper with constant ignition power.
Sounds weird but there has been no work done behind my dash before this problem started, and they were just barely making contact not like it had been physically put together.