1999 Chevy S-10 Factory Alarm

That's not a factory alarm.  If there was a factory alarm, it'd work like zargon says, but it uses the dashboard "security" lamp to indicate what it's doing----there's no LED.

If the alarm brain does say GM on it, that still doesn't mean it's factory installed----there are aftermarket alarms with the GM name on them, sold through the parts department.  Usually, these units get installed by aftermarket installers for the dealer's customers.

If you close the door and set the alarm....... do its other funtions still work?  Will it sound off if you open a door by hand?  Is the starter disabled?

If it's only the locks that aren't working, it shouldn't be too hard to troubleshoot that.  The lock wires in that truck are blue, and white, to the right of the gas pedal.  Look for the place where the installer connected to them, and then follow that wiring back to the alarm brain.  Inspect the connections, and test the lock outputs of the alarm.

White30, please make  your own post; no need to intrude on this one.

underground,

Have you had it for a long time and these problems just appeared.....or did you just buy the truck used, and this is what you found?

At my job, we mainly do dealer work, and we'll set up a system in pretty much any way the dealer wants.  Dealers generally sell alarms on the basis that you'll get an insurance discount because of the starter kill.  Also, sometimes customers are cheap and don't want to pay for all the features, or in other cases, they get freaked out by car alarms for whatever reason, but they still want the insurance discount.

What I'm getting at, is that sometimes the dealer will only want a remote-controlled kill switch.  Minimal cost, minimal complexity, and customer still gets his insurance discount.  But...... remote kill-only devices aren't common, and we don't sell one.  Instead, we'll just use a keyless entry system to activate the starter kill, but we don't hook up the keyless features.  And then, sometimes we even run out of keyless entry units.....which means we put in a full alarm system, but we delete the siren, shock sensor, and keyless-----we just put in the brain, starter kill, LED, and valet switch.

For what you're saying, it sounds like you have an alarm system in there, but installed as keyless only.  If you have the time and inclination, you could probably test the functions of the leftover wires, and hook them up.

Usually, the lock/unlock outputs are in a separate plug.  The plug may have two or three pins in it.  Use a meter to test those pins while operating your remote, and if they test right, hook them up.