I installed a Dakota box (According to "Steve R"s instructions) to my 75TS gearbox (3wire) and GTV6 speedometer (2wire), did not use the orig 75TS amplifier.
The instruction from "Steve R" was very good but on my car the 3 wires from the sender was different colours (Surprised!?

). My wires was:
Pink: 12v ...... Yellow: Signal ...... "No Cable Insulation": Ground
(It worked that way when I only used the orig.amplifier box anyway... the speedo read about x2 though..)
Now to the Problem:
As soon as the engine starts and the tachometer jumps up to around 1500rpm the speedo does the same and lays the needle at 40 km/h. If I rev the engine the speedo follows the tacho.
In the Dakota "Trouble shooting guide" they list 3 things that can cause my problem:
Speedometer will read when the vehicle is sitting still
Possible cause 1: Tach wire too close to speed signal wire
Solution: Route the speed signal and tachometer wires away fram eachother to aviod interference.
Done: Routed a new wire from the Dakota box to the speedo
Result: Nothing. Speedo still follows tacho
Possible cause 2: Signal IN and OUT routed to close
Solution: Route signal IN and OUT away from eachother to avoid feedback
Done: (Hard because the Input and OUT1 slot sits directly beside each other.) Tried using more shielded cables. Tested using OUT3 (Also AC as OUT1)
Result: Nothing. Speedo still follows tacho
Possible cause 3: Ground interference
Solution: Make sure the speed sensor and SGI-5 are grounded together.
Done: Checked grounding with multimeter, was ok.
Result: Nothing. Speedo still follows tacho
PLEASE HELP!!

What can I do??