Heard that its usually only a issue if you don't have a cruise control equipped car. In my 86 gt they are behind the radio for easiest access..on the 88 I think it's pretty easy to tap into them behind the kick panel..
6. VEHICLE SPEED SENSOR SIGNALS
These signals are required for cruise control and as stated earlier, some have reported stalling problems on cars not equipped with cruise so avoid the head-ache and just do it. These will also generate an error code in the EEC if not installed. These signals come from a sensor that plugs into the transmission. The easiest place to tap into them is behind the driver's side kick panel. There is an 8 pin connector cable which runs back to the driver's seat, across the floor under the seat then back towards the front of the car and then goes through the transmission hump to the sensor. You will need to splice into the orange/yellow wire. The other end of this signal needs an EEC pin attached and this gets inserted into the EEC connector into position 6. You need to splice into the dark green/white wire for the other connection. The other end of this signal needs an EEC pin attached and this gets inserted into the EEC connector into position 3. Refer to figure 2.
.....this is what I went off of. I don't know why sometimes it stalls and not others
