So I bought a 1994 F-150 XLT a couple months ago. It appears stock, except for a cheap aftermarket head unit. There is also a small antennae or something underneath the dashboard, but the previous owner did not tell me what it was. Other than that, it seems stock.

Today an alarm started sounding periodically every five or so seconds whenever the truck is running. I have no idea what it is, but it is definitely coming from behind/underneath the dashboard. Any ideas what it is, and how to deactivate it?

I uploaded a brief video showing the alarm in question.

 

I think you're supposed to breathe in a tube or something, to prove you haven't been drinking.

You haven't been drinking, have you?

 

Oh no, not today. Also aren't most breathalyzer systems sort of expensive, and usually not just left in a truck?

 

Lol!! No idea. Seriously, was joking initially but that might be what it is.

 

Sort of zeroing in on the stupid aftermarket deck. I'm going to try uninstalling or at least disconnecting it today. I am almost certain it has nothing to do with the truck itself, because I've had quite a few Ford trucks and haven't heard any of them make that sound before.

 

Sounds like an alarm system

 

not some kind of coolant level sensor?