Your 99 does not have a Univolt. If you have a monitor, check the voltage, if it is 13 volts or higher with the trailer plugged in, the converter is working. The converter that I installed in our Overlander (out of a 2005 model) only makes a noise if it works really hard and the cooling fan kicks on. And where it is, you have to open a cabinet door to hear that.
If you would like, there is a forums member that lives in Marco Island that would be happy to check over your trailer for you, and show you how everything works, for a nominal fee. I can PM you with his info.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.