Update for anyone in the future... For the Viper Model 300 pre-blue valet port with single grey wire valet toggle, the black wire from the toggle is simply the ground wire. The ignition interrupt wiring MUST be hooked up for the valet switch to work. That was my issue.

I have the same issue: re-installing a used alarm that has the grey valet wire coming from the main harness to a toggle switch. The switch then has a black wire that should be connected to...? There are only two ports on this older Viper 300; the main harness port and one port on the side for the lock/unlock wires. I've tried grounding the black wire put the valet toggle seems to do nothing and all manuals and advice online simply reference a port on the brain that simply isn't there on this (presumably very early) model. The case says "Viper Model 300". Any expert old timers?

Hello Jesse,
I am not sure what kind of a valet switch that you currently have for replacement, however all viper systems use a two wire connector, with one gray wire and one black wire and a blue connector on the end. All this does when you hit the switch is series, or connect the two wires. The brain reads the number of pulses that is receiving the specified timeframe and then completes the command based on the set number of pulses. This connector is a separate 2 pin connector from the 12 pin main harness. This will be located when looking at the 12 pin harness on the right side of the brain.