Thanks all. I'm sure I am just too inexperienced to see how these devices do what I'm after. I am not trying to switch anything with lots of current. Here is the issue -- I have an air flow sensor that produces a signal from o to 5vdc, depending on air flow. More flow, more voltage. That signal is used by my car's computer to meter out the fuel, etc. Separately, the car has a switch that goes to ground when the throttle is closed (and goes to 5v whenever the throttle is not closed). I want to intercept the air flow sensor wire and condition it so that (a) it simply follows the sensor voltage whenever the throttle is open, and (b) follows the sensors voltage when the throttle is closed, but only up to 1vdc. In other words, I want it to be a simple voltage follower whenever the throttle switch is high, and when the throttle switch is low I want it to be a voltage follower with an upper limit of 1vdc (so that if the sensor has .5vdc, the circuit will output .5vdc, but if the sensor has 1cdv or higher, the circuit will output only 1vdc). Suggestions?