The GV needs a speed signal for the Autodrive function which the automatic units have, which you don't need with the 5 speed, and it keeps the unit from coming on below 20 on both transmissions. In my old truck with the C6, I left the switch on all the time and OD would automatically come on at 45 mph and the unit would turn off at 20. My ZF-5 I turn it on manually when I need it and have to turn it off manually when I'm done and always when I come to stop- it won't turn off automatically. Here's what the manual says-
"The autodrive control box is fed a signal by the signal generator attached to the speedo cable. From the control box a signal is sent to the dash mounted green light, and then to the manual on/off switch, the signals final destination is to the solenoid on the GV unit. The unit activates once ground is supplied, so +12v should always be present at the solenoid when ignition is turned on."
So, it uses the signal to keep it from turning on below 20 mph as it has insufficient hydraulic pressure and you can damage it. That's why they say to not use it to split 1st and 2nd and never in reverse. However you still have to turn the hand switch off when you come to a stop which is stupid, so as long as you don't try using it below 20 you should be fine without the speed signal it uses to keep from powering up. IIRC the automatic box has a manual position on the switch, doesn't it?
)
