Wondering if I can i add cruise control on a 84 mercedes 500 sec euro that doesn't have the option installed are the connections there or do I need a new harness?

Just go aftermarket, it's cheaper, easier, and likely more reliable...

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Who makes one ?, or is that just a guess, on my 89 it was an electronic control unit. Euro versions are unique, there have to be some gray market cars that can be used as a donor