unplug the ecu connector and the vtec pressure connectors. take a ohm meter and put one lead on ground and the other on one of the pins on the pressure sensor connector. test both pins. one pin sould be a solid ground and the other pin should be open if you have the ecu connectors unplugged as well. if you have no ground check the ground location on the thermostat houseing and make sure it good. if that is ok i'd suggest running a ground wire from that connector to the thermostat houseing. if you have both that are grounded then you have a shorted wire. undo the ground on the thermostat housing and retest the connector to figure out wich one is now open circuit. the one that is still shorted is the wire that you will to trace and find the short. once you have found it and repaired the short remember to bolt the grounds back to the thermostat houseing and plug everything back in and you should be good to go.