Is the battery dead?
1993 Dutchmen Classic is a travel trailer or 5 wheel. There are many models. Here is the operator's manual link. It is nearly useless.
According to the manual, it has a "Power Center". What is the make and model of the Power Center?
Power center connects shore power to house circuits. There is a 120 volt to 12 volt converter. This supplies 12 volts to lights while on shore power. It appears to be working OK.
There is a heavy gauge wire from the battery on the tongue to the power center. Many Dutchmen trailers have a self resetting circuit breaker located near the battery. It is a small can with plastic closing it up. It has two heavy bolts for electrical connections.
Measure voltage across the two terminals on the can. Voltage across the two connectors should be zero volts (circuit breaker is closed and working properly). Voltage of 0.2 or more means breaker is open and has not self reset. I expect an open circuit breaker would show 0.6 volts when connected to shore power. It could be 12.7 volts without shore power. Replace the breaker.
Double check by jumping across the two breaker terminals when shore power is "off". Lights should be "on".
Some older 120 volt to 12 volt converters have two sections. One is for battery charging and the other is for 12 volts to lights. What is the make and model of the Power Center?
There may be a 12 volt inline fuse or fuses on the Power Center. What is the make and model of the power center?