redirect for login instead of msg=86

hi-
my client needs the site categories/product viewable by only logged in wholesale customers. so i used the setting in the control panel at the category level to restrict to wholesale only, but i'd like the redirect when a non-logged in customer tries to click on a category to be to a login page, NOT msg.asp?message=86 as it defaults. i tried to find where this is even happening, but i didn't. any advice on where to look to change this default behavior? thanks!

you know, you might think so. but there's always a weird exception... thanks. i've peppered the code minimally with that type of logic now, just commented the code so when someone wants to un-do this, LOL, they can.