Compressor won't stop running

My train horn compressor won’t stop running. I had not used my truck in over a year and I recently got it up and running with new battery and all. This morning when I connected the train horn wire to the battery it just kept running. I wonder if it is because it had not been used in a long time? Any help is greatly appreciated.

Try checking your relay. 9 times out of 10, its that.

If you’re building air pressure to a point that your safety valve pops, then it’s a faulty relay or pressure switch. If you’re not building tank pressure then you’ve got a leak … Check valve can be a prime culprit.

Thanks, y’all have been a great help.