car is an 88 civic hatch with jdm b16a gen1 swap

using cable vss in the cable tranny with the original jdm b16 ecu

my question is: why is the car throwing the vss code?

i understand that the jdm siR's that use this motor,tranny, ecu use an electrical vss so thats where the vss signal for pin B16 on the ecu comes from... but on this car it still has the cable vss because it still has a cable driven speedo.... the yel/red wire coming from ecu pin B16 is spliced to a grn/wht wire that is run somewhere but i dont know where... when this swap is done, what is pin B16 connected to to give the ecu a signal so that it knows the car is moving and vtec can engage?

i have searched, i have looked in the civic/crx faq2.0 but there was dead links... so plz just offer the help if you have it... thanks!