Ok I have the PMDG 737-700 cold and dark.I hit electric power, stand-by power and then ground power. Then next thing is APU generator start.APU powers up, then needle drops. When the blue lights come up on the APU Gen lights and I try to turn the switches off, they both fail to go out. I can click and click, but they do not go out.Sometimes they go out on the first or second click. Most of the time, they don't go out right away.Thanks

Please sign your full real name to your posts per PMDG forum rules, thanks.If you're already on ground power you don't need the APU... that's probably your issue.

You need the APU to supply a pneumatic source to spin/start the engines, at least one of them. I've never noticed the NG's to allow a ground air source such as even a tug air source emulation.I don't recall the exact procedure but check your bleed air switches so they are not on the APU until it is revved up to prevent compressor load during APU start.There are two positions for each electrical bus transfer - APU and GEN. GEN is the engine supplied power after it has been started and stabilized. Ground power will disable as soon as you release the parking break.Anyway, I have always succeeded in transferring from ground power to APU power before releasing the parking break and pushing back. Since I am too busy during push back, I don't start the engines until push back completion. At many airports engine starts near the terminal are not allowed due to air and noise pollution plus the greater chance of engine debris ingestion near gates.It is also the policy of some airlines, particularly in heavy precipitation, to keep the APU running through the initial climb. On arrival r/w the APU is started up during taxiing in by the PNF.