6NZ fan not engaging

Having some issues with a 6NZ82245 in a 1995 FLD 120. Temp gauge runs up to 185+, overtemp light and buzzer comes on, truck wants to shut down. Fan never engages. Put a manual switch in, so I know that the air switch on the fan clutch works ok. Have talked to my Cat man, and several Freightliner dealers, and getting a few different responses. I'm thinking that the 2 sensors behind the A/C compressor are at fault, which should be the fan switch and the gauge sensor. Was told that these are truck specific, so go to the truck dealer and not Cat. One Freightliner parts man mentioned that the A/C pressure switch may be at fault, however a/c on this truck is inop at the moment. The other Freightliner parts man mentioned 3 sensors, a fan sensor, gauge sensor, and engine temp sensor. I'm wondering if he may have something confused on this one. Anyone have any ideas? Hoping I'm not running into an ECM issue. 217 is cut in on the fan, but gauge isn't going that high before the light comes on.

 

Where is the light switch located? I'm tempted to put a manual gauge in just to make sure that the dash temp is reading correctly. I would hate to get it too hot.

 

Good thoughts! One sensor is 2 wire other is 3 I think. One supposed to be for the fan other for the gauge. Have to search around for one for light. Wasn't sure if the light went through the ecm or not.