Honda Accord 1990 Cooling fan trouble

Hi, I have a 1990 Accord and am having a problem with the cooling fan,
I will turn off the engine and the cooling fan will stay on. after
about 15 min. the fan will shut off then come right back on again. this
pattern continues until the battery is drained. I have read some of the
other posts in this group and have pretty much narrowed it down to two
possibilitys either its a problem with the fan timer or the switch B
sensor is malfunctioning. Does anyone know how I can figure out which
one it is.(I'm leaning towards the switch b sensor since the timer
seems to be turning the fan off after the appropriate 15 min.) (I don't
have air conditioning so its not the condenser fan)

 

It's most likely the switch.