hi i do have a probleme with a f-150 2000
the light goes on alone with no key's inside
this situation became at low temperature and hi humidity ( freezing point and below ) . at low temp like -15 deg celcius (5 deg farenheight ) the probleme it's not showing... at all .....
i tink the ignition switch is the probleme but i'm not shure at 100 %....tank's ...

 

It would be a good idea if you mentioned WHICH light....

Assuming the interior/cabin lights, it's probably a sticky door switch.

SEARCH "DOOR AJAR" or "WD-40".

Steve

 

sorry !! all the exterior and accessories ( radio fan light ext. , )
the truck is in the street and sudunly, exterior light open by itself .......
after a few minute goes off by itself and the trouble reappeare again during the day .....