The "WAIT"light should only illuminate when the key is ON and the engine is OFF. As soon as you turn the key to ON, it should go out and stay out whether the engine is cold, hot running or stopped. I'm too full of turkey to try and muddle through to an answer for why it is on when the engine is running. Go get another beer and it won't seem so important....
Both generator lights should illuminate when the key is ON and the engine is OFF and when the engine is first running but has not run at high enough RPMs to make full power. If it illuminates at any other time you have some troubleshooting to do. If you follow the instructions on the back of the driver sun side visor and put the pedal half way to the floor when it is above 32 degrees outside and all the way to the floor when it is below 32 degrees the engine should rev enough on starting to extinguish the generator lights. Note that the instructions on the visor and in the Operator Manual do NOT distinguish between a cold engine or a hot engine. However if, like most of us, you start a warm engine without benefit of extra throttle, you may have to rev the engine to extinguish the lights.
For LTWVARNG, your truck had a light socket when it was made. The bulb is a bayonet style that pushes into the socket and the socket twists into a cam lock behind the dash. Remove the screws that hold the dash panel, tilt it forward and go hunting. That is a lot easier than standing on you head with a flashlight looking from below and you won't spill your beer.
194 style lamps are available in different wattages. We have worked on some trucks that needed to have lower wattage lamps installed to keep them from blowing. In 25 years we've never been able to isolate a single specific cause that could be fixed to prevent it so, if the lamps keep blowing do a quick online search for lower wattage lamps. If it's a problem finding them, post a reply or PM me. My son Chris probably knows the available wattages and lamp numbers off the top of his head.
Don't worry about making more noise with a straight through muffler. Most of the noise from the the engine is just that, engine clatter and the exhaust difference won't matter.
Lance