yes another speedo wiring question, this one a little different and unique.

[b00stinbmx]

ok heres the deal. 1990 s13 hatch previous automatic now manual with a rb20det, just installed a KA manual speed sensor finally cause i was sick of no mph readings. i was using the DOHC KA lower harness so the speed sensor pluged right in. now heres the weird part. when i start to drive the speedo pretty much just climbs right up to 50 mph and stop sthere. dosen;t move. even if im only going like 10mph, as soon as i move the car it just climbs and stops. im DEF missing something, but i thought the wiring just went straight from speed sensor to speedometer, either that or this stock gauge cluser is f'd. I have a rigged maxima tach in there right now but all other gauges and lights do work. and this is the 2nd speed sensor i have tried so we can rule that outta the question. please any help is appreciated. i've searched, and i've read my fsm. no help so far im a lil stumped just seeing if anyone else had this prob.