76 Eldorado - stop engine light
 

I own a 1976 Eldorado Convertible. Since a few weeks the "stop engine - temperture" light remains on even I disconnect the 18 light green wire at the metal temperture switch at rear of left cylinder head. Obviously the 18 light green wire and terminal No. 6 of the printed circuit connector is grounded.

What shall I do? Please do not tell me I should just disconnect the lamp! At this moment I have to disconnect the negative battery cable since the lamp fails to go out ...

Any help appreciated!
Kind regards from Switzerland!
Karl