[200q20v] Busted temp sender, or gauge?

[Rob Winchell]

My coolant temp gauge has been all crazy for the last month or two.
Sometimes it works fine, sometimes it's just dead (pegged at bottom). I sort
of assumed this was the multi-function temp sender going bad. However, the
fan still comes on at appropriate times. What tells the fan the engine is
hot and needs to go on, if not the temp sender?

Thanks,
Rob Winchell
91 200Q