[Threshold]

Try this:

pawn Code:

new Neon1[MAX_VEHICLES]; //Used for the neon object
new Neon2[MAX_VEHICLES]; //Used for the second neon object
new NeonAttached[MAX_VEHICLES]; //Used to set whether a car has neon attached or not

public OnVehicleSpawn(vehicleid)
{
    if(NeonAttached[vehicleid] == 1) //If the vehicle has neon attached
    {
        AttachObjectToVehicle(Neon1[vehicleid], vehicleid, 0.8, 0.0, -0.70, 0.0, 0.0, 0.0);
        AttachObjectToVehicle(Neon2[vehicleid], vehicleid, -0.8, 0.0, -0.70, 0.0, 0.0, 0.0);
    }
    return 1;
}

CMD:addneon(playerid, params[])
{
    if(PlayerInfo[playerid][pAdmin] < 3) return SendClientMessageEx(playerid, COLOR_RED, "You do not have permission to use this cmd.");
    if(GetPlayerState(playerid) != PLAYER_STATE_DRIVER) return SendClientMessage(playerid, COLOR_GREY, "You are not in a vehicle as a driver.");
    if(NeonAttached[GetPlayerVehicleID(playerid)] == 1) return SendClientMessage(playerid, COLOR_GREY, "This vehicle already has neon attached, use /removeneon to remove it.");
    new vehicleid = GetPlayerVehicleID(playerid);
    Neon1[vehicleid] = CreateObject(18648,0,0,0,0,0,0,100.0); //Create the first neon object
    Neon2[vehicleid] = CreateObject(18648,0,0,0,0,0,0,100.0); //Create the second neon object
    AttachObjectToVehicle(Neon1[vehicleid], vehicleid, 0.8, 0.0, -0.70, 0.0, 0.0, 0.0);
    AttachObjectToVehicle(Neon2[vehicleid], vehicleid, -0.8, 0.0, -0.70, 0.0, 0.0, 0.0);
    SendClientMessage(playerid, 0xFFFFFFFF, "Neon lights have been installed on this vehicle..");
    NeonAttached[vehicleid] = 1; //This vehicle has neon attached
    return 1;
 }

CMD:removeneon(playerid, params[])
{
    if(PlayerInfo[playerid][pAdmin] < 3) return SendClientMessageEx(playerid, COLOR_RED, "You do not have permission to use this cmd.");
    if(GetPlayerState(playerid) != PLAYER_STATE_DRIVER) return SendClientMessage(playerid, COLOR_GREY, "You are not in a vehicle as a driver.");
    if(NeonAttached[GetPlayerVehicleID(playerid)] == 0) return SendClientMessage(playerid, COLOR_GREY, "This vehicle doesn't have neon attached, use /addneon to add it.");
    new vehicleid = GetPlayerVehicleID(playerid);
    DestroyObject(Neon1[vehicleid]);
    DestroyObject(Neon2[vehicleid]);
    SendClientMessage(playerid, 0xFFFFFFFF, "Neon lights have been removed from this vehicle..");
    NeonAttached[vehicleid] = 0; //This vehicle no longer has neon attached
    return 1;
}