Not sure if anyone ever documented this, but I found a temperature sending unit that will close (turn on) around 225 - 240 degrees. Which IMO is perfect to trigger an idiot buzzer that goes off when the car gets too hot.

Bi-Metal Type, Radiator Fan
Switch 3/8 -18Dryseal Thread,
Normally open Closes @ 223 to 239¢K
Ford: E0ZZ-8B607A
Wells: SW501
Standard: TS-121

The 'normal' Ford sending unit for an idiot light has a range of 250 to 260 degrees

Bi-Metal Type, Light Switch
3/8" -18 Dryseal Thread,
Normally open Closes @ 250 to 260 ¢K
Ford: C8GY-10884A, D1FZ-10884A,
D6AZ-10884A, E43Z-10884A
Wells: TU32
Standard: TS36.

These will fit most pushrod V8 Fords, and probably some I4/V6.. Not sure on newer stuff...

and these have a different thread pitch than GM.