Recently bought a 92 500SL. Had it a short time and the interior lights stopped coming on, regardless of the switch position. I also can't activate the door locks remotely or the security system. Is there a common thread here? The pump module makes noise, but doesn't seem to draw a vacuum. I don't have a hand pump to test it.

Since none of the doors, trunk or fuel filler panel seem to be working, I was going to replace the pump module as a first step to fault isolating the problem. Does anyone have experience with these faults and recognize the source of the problem?

 

check the pse pump under the hydraulic pump. it should be cased in foam. sometimes the hydraulic pump leaks onto the pse pump. does your top work. the pse pump controls locking, cental lighting, and etc. check for fluid damage. pull the connectors off and check for corosion.

 

I pulled out a pump encased in foam located in th trunk above the battery. It has many pneumatic lines running off of it. Is that the PSE pump? I pulled off a couple connectors and don't find any vacuum when it's energized. No signs of leakage from the hydraulic pump. I was going to hook up a vacuum gauge. what do you think?

 

How does a vacuum pump control central lighting anyway? Can't see the connection between the interior lights malfunctioning and this pump. I'm inclined to replace the pump, but I'd like to be ure one of the lines isn't leaking.

 

There is a control module built into the pump, how do you think it controls where the vacuum is routed. The pse pump controls central locking,ata (anti theft alarm), manifold vacuum assist, it even control the signal to your rear window defroster. anyway back to your question if the pse pump control central locking, it gets a signal from a door switch, the black pin that pushes in when you close your door. that signal goes to the pse pump/control module which makes it an input signal, then the pse pump sends an output signal to the interior lights. I see that you can't operate the locks remotly. can you operate the locks using the interior switch, if so that rules out a vacuum problem.

 

do the lights work when you switch them from auto to always on, if not i would check the fuse. the part with the pse controling them only applies to the auto feature. they should turn on manualy. also if your interior locking switch works don't rule out your key. the batteries in your key could be dead or you may need a new key. they tend to have their problems too.

 

The pump has no control over lighting or the window defroster!!!

Power for the overhead lights comes from fuse #9 in the main fuse box. Assuming the fuse is good, you may have a problem with the rocker switches or the control module in the assembly. If you send me an email, I can reply with a schematic.

 

Fuse #9 is good. All the interior lights are out (including the door lights). If I'm not mistaken, I think the center light module is controlled by the rocker switch, but the door lights are controlled by the door jamb switch. That schematic would be good to troubleshoot with.

On the central locking issue, I think its the vacuum pump that's the bad actor here. I'm going to troubleshoot it with a vacuum gauge. The only question I have is if there is a leak in a line somewhere, would that result in a loss of vacuum on all the ports or only if the one disconnected and plugged is the leaky line?

 

The circuit for the door lights is very simple: fuse, light, door jamb switch to ground. So if fuses are good, then the jamb switch(es) are bad. A check of the switch would be whether or not the seat controls operate with the door open and the key off (they should).

A leak in one vacuum circuit would affect all circuits that the pump is applying vacuum/pressure to.

 

Similar problem on my '91 500SL.All interior lights/overhead console switches and lights/power seat switches all work correctly when key removed and the passenger side door is opened but the interior lights do notturn onand power seat switches do not work when the driver's side door is opened. The overhead console switches all seem to function properly. I swapped the door swithes andpass sidefunctions correctly with the driver'sswitch, but the driver's side still does not work.

I've searched and did not find a solution, any ideas appreciated. BTW, great board - I've found many answers without posting.