VSS wire working intermittently on Supra

1994 Toyota Supra (the non-turbo version) with a pioneer AVIC-D1 recently installed. (did the lockout bypass moving the unused cellphone mute wire over to the empty spot next to the ground on the harness)

So, i recently installed the AVIC-D1 for  a buddy (i was an installer for about 5 years, but quit a few years ago for a new career) and everything worked perfectly after the install. i tested it out, test drove it, and the nav worked fine.

the next day he calls me saying that sometimes he will take off from a stop light and the arrow wont move. he says it sometimes will still be sitting at an intersection he was at 5+ minutes ago, meanwhile he is miles down the road. then all of the sudden it will jump and catch up with him. well, a week went by but i ididnt get around to fixing it right away, but by the time i did (today) the arrow stopped moving with the car totally. the arrow spins as you turn(gyroscope), but doesnt move forward as you drive(vss).

so today, i take it apart to troubleshoot. i hooked up the meter to the vss and drove it around a bit. the VSS is sending out voltage intermittantly (spelling?). (i tapped into it down in the passenger kick at the ECU when installing the HU)

so, i hooked up the fluke meter and its around 7 volts AC, fluctuating up and down as we drive. then sometimes it will just stop and go down to less than 1 volt as we are driving. so i redid the connection and things seemed to be ok. we test drove it a few times, it worked. perfectly (again, just like the first time... blah)

then, we put it back together (just like last time) and when we were all done, as he was driving away he informed me that the arrow wasnt moving again. he had to leave because he had dinner plans, so we didnt look into it any further. anyways, im supposed to look at it tomorrow again but im stumped.

any clue why this wire wont stay consistant? ive hooked up 100's of nav systems and remote starts in my day, and searched for 100s of tach and vss wires. no doubt i have the correct wire. and no doubt the connection is secure. i checked and rechecked.

have any of you ever run into this problem before? any suggestions would be greatly appreciated!

i will try that, and you may be right - but -

i hooked up my meter as we drove, and when the voltage worked on the VSS wire, the nav worked, once the voltage dropped from about 7 volts to less than 1 volt, the nav stopped working. this is what leads me to believe it is the VSS wire.

however, next time i have the car i will check the connection screen

keep the ideas coming!v