[ESS] Help setting key binding for ess

[Seth Falcon]

I would like to map C-= to ess-smart-underscore and have my underscore
key just insert underscores.

Can someone give me a hint as to which hooks I need to add to?

I tried:

(add-hook 'ess-mode-hook
          '(lambda () (setq fill-column 80))
          '(lambda () 
             (progn
               (define-key ess-mode-map [?\C-=] 'ess-smart-underscore)
               (define-key inferior-ess-mode-map [?\C-=] 'ess-smart-underscore)
               (define-key ess-mode-map "_" nil)
               (define-key inferior-ess-mode-map "_" nil))))

But it isn't working.  Also, when editing Sweave files, even if I do
local-set-key in an R chunk, by the time I move to a different chunk,
my binding has been reset :-(

Help, I'm about to start using '=' instead of '<-'

+ seth