I have a Bryant, Day & Night, gas furnace model 394GAD which approximately 20 yr old. It works fine except for wasting gas due to the manual pilot continuously lit. I would like to install a automatic ignition system. Does anyone have any experience with this? Do you know the model number, etc. that goes with this furnace? I would like to do it myself.

It is not really a do it yourself project. You have to install a new gas valve and all kinds of wiring then you have to change the pilot lite and then the gas valve has to be adjusted with a special tool. Your furnace is 20 years old. Why put money into it when you can get a new high efficiency unit and save big time on your gas bill.