When you turn on the truck is the pump comping on-can you hear it running? If it is and if it keeps running then you should be able to look under the back of the truck and see where the air is getting out of the bags. There may be a crack in one of the bags or there are solenoids at the top of them that may also leak. If you can't see obviously where the leak is you could spray soapy water and watch for where it bubbles up to find the leak. If the pump is not coming on then you can check it with a test light to see if power is getting to it. If it is and the compressor is not running then you proabably have a bad compressor. If it isnt then you can check the fuses for the system, if you get to that point and still havent found anything then I can post more diagnostic info for you to check farther into the system.
Hope this helps, let me know what you find out.
Thanks for using JA
Thanks for accepting. Do you notice any difference in the sound you hear from when it was working?