Is the sensor/switch in the T-stat housing with 3 terminals for turning the fan on/off?

No continuity between any terminals nor between any terminal & ground.

The sensor sitting vertically in the water passage of the intake manifold w/2 terminals (front-drv side of engine under the air filter) is for the electric fan?
If so then the resistance of the sensor is 2.51k @ 90-95F ambient air temp. Tested it when I got home after a long hot day in the driveway, coolant must be at least that temp. Tested again next morning w/ambient air at 75F, resistance up to 4.1k

From what I have seen on other posts the resistance is too high. Replace?

Where is the fan relay?

I see mention of an A/C lock out sensor in the parts section, is it what I think it is? Cuts off the A/C when the engine temp is too high? Or am I thinking too much?
I also see an Aux Fan Switch (1 terminal) mentioned that looks like the sensor mounted next to the 3 terminal sensor in the t-stat housing (it also looks like the A/C lock out switch). No continuity here either between terminal & gnd at 90-95F ambient air temp.

Thanks

K

__________________
1999 E320 (gave to daughter) 250K
1994 F150 (may be the end of its road) 240K
1989 560 SL (Reassembly after paint job) 160K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (still running strong with an upgraded cam) 349K
1986 242Ti (deceased)
1968 GT500KR (under restoration)