This is my first time scripting something like this, I'm not used to RemoteEvents or functions. I've tried everything to my knowledge and I just couldn't figure it out myself. Can someone tell me if I'm missing things, or doing something wrong, cause I know I am?
Original Local Script:
local mouse = game.Players.LocalPlayer:GetMouse()
local Bus = game.Workspace:findFirstChild(game.Players.LocalPlayer.PlayerGui.TGUI.Value.Value)
mouse.KeyDown:connect(function (key)
key = string.lower(key)
if key == "q" then -- LEFT SIGNAL
Bus.Model.Bodykit.Blinkers.D40LFR1.LeftEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.LeftEnable.Value
Bus.Model.Bodykit.Blinkers.D40LFR1.RightEnable.Value = false
Bus.Model.Bodykit.Blinkers.D40LFR1.HazardEnable.Value = false
elseif key == "e" then -- RIGHT SIGNAL
Bus.Model.Bodykit.Blinkers.D40LFR1.RightEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.RightEnable.Value
Bus.Model.Bodykit.Blinkers.D40LFR1.LeftEnable.Value = false
Bus.Model.Bodykit.Blinkers.D40LFR1.HazardEnable.Value = false
elseif key == "x" then -- HAZARDS
Bus.Model.Bodykit.Blinkers.D40LFR1.HazardEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.HazardEnable.Value
Bus.Model.Bodykit.Blinkers.D40LFR1.LeftEnable.Value = false
Bus.Model.Bodykit.Blinkers.D40LFR1.RightEnable.Value = false
elseif key == "k" then -- KNEEL
Bus.Model.Bodykit.Blinkers.D40LFR1.KneelEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.KneelEnable.Value
elseif key == "m" then -- FRONT DOOR OPEN/CLOSE
Bus.Model.Bodykit.Blinkers.D40LFR1.FrontEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.FrontEnable.Value
elseif key == "n" then -- BACK DOOR OPEN/CLOSE
Bus.Model.Bodykit.Blinkers.D40LFR1.RearEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.RearEnable.Value
elseif key == "l" then -- HEADLIGHTS
Bus.Model.Bodykit.Blinkers.D40LFR1.HeadlightsEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.HeadlightsEnable.Value
elseif key == "j" then -- INTERIOR LIGHTS
Bus.Model.Bodykit.Blinkers.D40LFR1.InteriorEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.InteriorEnable.Value
elseif key == "r" then -- REVERSE
Bus.Model.Bodykit.Blinkers.D40LFR1.ReverseEnable.Value = not Bus.Model.Bodykit.Blinkers.D40LFR1.ReverseEnable.Value
end
end)
Modified Local script:
local key = game.Players.LocalPlayer:GetMouse()
local event = game.ReplicatedStorage.BusEvent
local Bus = game.Workspace:findFirstChild(game.Players.LocalPlayer.PlayerGui.TGUI.Value.Value)
event:FireServer(key)
end)
(RemoteEvent is in ReplcatedStorage named "BusEvent"
New Server script:
local event = game.ReplicatedStorage.BusEvent
event.OnServerEvent:Connect(function (key)
key = string.lower(key)
if key == "q" then -- LEFT SIGNAL
Bus.Model.Bodykit.Blinkers.DriversCab.LeftEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.LeftEnable.Value
Bus.Model.Bodykit.Blinkers.DriversCab.RightEnable.Value = false
Bus.Model.Bodykit.Blinkers.DriversCab.HazardEnable.Value = false
elseif key == "e" then -- RIGHT SIGNAL
Bus.Model.Bodykit.Blinkers.DriversCab.RightEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.RightEnable.Value
Bus.Model.Bodykit.Blinkers.DriversCab.LeftEnable.Value = false
Bus.Model.Bodykit.Blinkers.DriversCab.HazardEnable.Value = false
elseif key == "x" then -- HAZARDS
Bus.Model.Bodykit.Blinkers.DriversCab.HazardEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.HazardEnable.Value
Bus.Model.Bodykit.Blinkers.DriversCab.LeftEnable.Value = false
Bus.Model.Bodykit.Blinkers.DriversCab.RightEnable.Value = false
elseif key == "k" then -- KNEEL
Bus.Model.Bodykit.Blinkers.DriversCab.KneelEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.KneelEnable.Value
elseif key == "m" then -- FRONT DOOR OPEN/CLOSE
Bus.Model.Bodykit.Blinkers.DriversCab.FrontEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.FrontEnable.Value
elseif key == "n" then -- BACK DOOR UNLOCK
Bus.Model.Bodykit.Blinkers.DriversCab.RearEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.RearEnable.Value
elseif key == "l" then -- HEADLIGHTS
Bus.Model.Bodykit.Blinkers.DriversCab.HeadlightsEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.HeadlightsEnable.Value
elseif key == "j" then -- INTERIOR LIGHTS
Bus.Model.Bodykit.Blinkers.DriversCab.InteriorEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.InteriorEnable.Value
elseif key == "r" then -- REVERSE
Bus.Model.Bodykit.Blinkers.DriversCab.ReverseEnable.Value = not Bus.Model.Bodykit.Blinkers.DriversCab.ReverseEnable.Value
end
end)
This script will execute commands to other scripts within the model. This is the only local script I have an error with.

3 comments
The first parameter to OnServerEvent is always the player. So like 5 in your server script, key is the player. Don't pass the mouse either, that will error.
I've updated the question as I included the original local script. What do you mean by pass the mouse?
What they mean by passing the mouse is passing the mouse to the event/serverscript and like they said the player is automatically passed to the serverscript