[T3] An old flasher problem I've never been able to figure out

[Marklist]

71 Manual FI

My signal flasher only works intermittently.  It usually doesn't work at 
night or the really early morning.  When it does work at night is 
usually during the summer or Santa Anas.  But there is not a 100% 
correlation.  I had this problem with a bug when I was a kid.  I've had 
this problem with another Type 3.  I've changed the flashers several 
times and the problem persists.

I'm thinking that is has something to do with ambient moisture, but it 
is not enough to produce any noticeable condensation.

Any Ideas?