Land Rover Repair: Cruise control on 96 Disco I, vacuum lines, digital stream

Question
Sir,

Cruise does not work.  Vacuum lines replaced,Brake switch,transducer and actuator are good, ECU rebuilt. I am curious about the VSS input for the cruise ECU.  When I check it with a multimeter I get 7.8 volts constant. Speedometer shows 5 miles per hour slower than GPS speed, but is consistent.  any ideas what else it could be?

Answer
You have done all the common things.  99% of cruise problems are indeed the vacuum lines or the switches.  If you have swapped the ECU as well you are running out of things to try.  The speed signal is a digital stream I believe, so you can't evaluate it with a multimeter.  The only way I know to test that system is with the factory T4 tester,  The Autologic does not have a test sequence for cruise.

I am really not sure what else to suggest except seeking out a shop with T4.  You seem to have changed all the problem parts, so you either have an esoteric wiring issue, or one of the supposed "fixes" is wrong.