Suburban NT24 SP

Trace your gas line. If there is a valve, it will be inline somewhere. Many of these little furnaces did not have an on/off valve.

They have several safety features, including a limit switch, sail switch and thermocouple. (some ignitors have a built in flame sensing feature; in that case no thermocouple)

To start this type of furnace, you need 12.6 volts or more. If the voltage is low (say 11.8) the fan doesn't run fast enough to close the sail. Turn the thermostat to 80. Within 30 to 45 seconds, the fan should start. Once the sail closes, the gas valve will open and the ignitor sparks. Some furnaces have a "one try" circuit board, others a "three try" board, which means it will try to light once or three times before shutting down. The fan will continue to run, but the furnace is not trying to light. Hope this makes sense.

You should be able to see the ignitor spark thru the little glass viewer. Also, you can hear it from the exhaust on the outside of the trailer.

You can repeat the above several times, letting the fan go off before the next cycle. If it really won't light, I would take the board in for testing. There are other items that cause failure as well but start with the board.