http://www.blazt.biz/products/cable.php
plugs into laptop, its nice and affordable too. Plugs into nissan consult port which did not come on 89 240s iirc. However, it should work with the sr20det, you'll just have to cut a consult port out of a newer nissan and wire it up to your ecu. PM me if you need more details, I just did this recently myself.