You installed an air horn on your truck and it has a small electric compressor but cant generate fast enough as the alarm honks is there some sort of device you can put to make stay on?

The problem isn't a lack of a "stay-on" device; it's that your small compressor can't keep up with the air demand of the air horn. A "stay-on" device would just keep the compressor running continuously, which would likely lead to the compressor overheating and failing, or even the horn not working correctly because of insufficient air pressure.

You need a larger compressor or a different solution altogether. Here are a few options:

* Larger compressor: This is the most straightforward solution. Find a compressor capable of supplying the air volume needed by your air horn. You'll need to know the cubic feet per minute (CFM) rating of your horn to choose an appropriately sized compressor.

* Larger air tank: Adding a larger air tank will allow the compressor to build up a reserve of air, giving it time to recharge between horn blasts. This would work best in conjunction with a larger or more efficient compressor.

* Different horn: Consider using a smaller, less air-demanding air horn.

* Different type of horn: Explore alternatives like an electric horn (which doesn't require a compressor) or a pneumatic horn with a higher-capacity system.

Adding a simple "stay-on" switch will only prolong the problem; it won't solve the root cause of insufficient air pressure. You must address the compressor's inadequate capacity. Improperly modifying the system to force it to run continuously could lead to damage and potential fire hazards.