I have a 1993 SL500 in which the automatic locking feature is now inactive. The infra red appears to work fine and no blown fuses, however, none of the locking devices function (worked previously). Is there a relay in the circuit that may be non-functional, and if so, where is it located (any ideas)?

For clarification, how do you know the infra-red is working correctly?

I'm assuming the infra red is functioning okay since the lights on the doors illuminate and the interior lights turn off when attempting to lock the doors. However, none of the locks activiate (trunk, doors, etc.)??

To lock or unlock the car the infrared controller signals the vacuum/pressure pump. Both are located in the right-side of the trunk above the battery.

If your car locks properly with the key and lock, then your pump is probably good and the problem with IR operation may be the control signal to the pump.

You can lock and unlock doors, trunk, etc. using a key one at a time which I assume is strictly a mechanical function. Ive previously looked above the battery and verified the fuse located on top a relay is okay. I was thinking it could possibly be one of the two components located there. Both appear to be relays. I'm assuming the infra red transmits a signal to the trunk and that in turn activated a relay activating all the locks??? Open to suggestions and/or see the local dealer!!

Seems your pump never runs. Its fuse is in the fuse box in the trunk; and if it's good, then the pump is probably bad.

There are no relays associated with the locking system. The relay near your battery is for the fuel pumps.

You can hear the pump running in the trunk when you activate the infra red system at a door, trunk, etc. so I assume the pump is functional (sounds the same as when the system functioned). Where do you go from here? Day phone (815) 568-4378 NW of Chicago Would a broken line shut down the whole system?

It could.

You should check all the vacuum lines that leave the pump for leaks. You can use a vacuum pump available on loan for free at Autozone, or you can buy one for about $30.