Power Locks Unlock but don't Lock
 

For some reason both of my power lock switches will unlock the doors but will not lock them.I don't have keyless entry. I would think this might be the relay and not the actuators or switches since the doors unlock fine. Does anyone know where the relay is located on a 98STX. Any help or ideas on how to fix this problem would be greatly appreciated.
Thanks Jimmy V.
98 F150STX V6 Auto

Mine too
 

My 98 does the same thing. Only it does it when it's warmer out. Lately it works fine. Let me know if you find out what causes it.