I have a 1989 accord service manual but it doesnt really tell me where it is. All it says is that its above the interior fuse box but i cant see under there lol

Not really above, more like behind the fuse box. Take a flashlight and look under the dash "kind of behind and to the outside" of the car......there will be a grey/white box. From looking at my 89 LXi, it looks like you could get the "13 pin" connector out without removing much if anything,,,,that would allow testing of the inputs pretty simple.

PS - on mine the box even had "cruise control" printed on the grey/white box :)