Technical 1973 Fiat 850 Spider mystery wire

[J Banel]

What dose this yellow wire extending out of the upper heater hose fire wall passage connect to?The wire is about 18 inches long with a terminal ring on the end… also what is the function of the switch on the engine compartment sidewall?
( see attached pictures)
Thanks

 

[khnitz]

The switch on the side of the engine bay is to trigger a high idle speed for tuning, if I recall correctly.

 

[timmycm850]

It's likely a wire for the alternator that needs to be fitted. If not then it could be an earthing wire for the fuel tank.