SL/R129: Quick help with soft top limit switches
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Newbie
Joined: Oct 2011
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From: Palm Beach, Florida
1998 SL500
Quick help with soft top limit switches
1998 Sl 500
Seeking confirmation that the limit switch circuits controlling the RST sequencing are either in open (ohmmeter reading infinity) or closed position ( reading near 0 resistance). Trying to problem solve my top which hangs up on opening at the raised tonneau cover step. Suspect a faulty (shorted) limit switch (S84/5 - ST compartment cover open switch A 208 820 22 10) which reads continuity when open. Thanks!
Seeking confirmation that the limit switch circuits controlling the RST sequencing are either in open (ohmmeter reading infinity) or closed position ( reading near 0 resistance). Trying to problem solve my top which hangs up on opening at the raised tonneau cover step. Suspect a faulty (shorted) limit switch (S84/5 - ST compartment cover open switch A 208 820 22 10) which reads continuity when open. Thanks!
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Joined: Jan 2006
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From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
To confirm a motion has completed the signal from any limit switch should short to ground.
Thread Starter
Newbie
Joined: Oct 2011
Posts: 6
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From: Palm Beach, Florida
1998 SL500
Thank you Bob - you are legendary on this forum from all I've read. Short of disassembling the passenger seat to get at N52 for definitive testing, since the switch in question is readily accessible for testing directly could you clarify what ohmmeter readings I'd see at the switch if you happen to know? Shorting to ground implies to me that the switch circuit is completed and would test (near) zero resistance. I understand this approach doesn't take in to account all of the wiring and connections. Thanks again!
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Joined: Jan 2006
Posts: 1,982
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From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
With the compartment cover fully open the resistance across the limit switch contacts should be one ohm or less. In any other position it should be infinite.
The N52 controller is easy to access. It concealed beneath a cover in the floor of the storage compartment located behind the passenger seat (U.S. car).
The N52 controller is easy to access. It concealed beneath a cover in the floor of the storage compartment located behind the passenger seat (U.S. car).
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
Since the cover open switch is okay, if the sequence still quits I would perform a comprehensive check of all of the limit switch inputs. The procedure is here.
Thread Starter
Newbie
Joined: Oct 2011
Posts: 6
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From: Palm Beach, Florida
1998 SL500
Fixed! Well that RST controller is very interesting. And Bob you were right (of course I had no doubt)- checking for other faults led to the drivers side window regulator as the culprit. The interesting part is that when I initiated the sequence to put the top down, both windows would begin to go down together (seemingly normally and symmetrically) and PRIOR to the windows being fully down the rear bow would raise and the rear tonneau cover would unlock and open appropriately. To complete this part of the sequence only takes a few seconds while the windows continue their downward travel. Once fully down the window regulator must send some signal to the controller to carry on with the sequencing. In my case a faulty regulator failed to send such a signal at that instant and so the sequence stopped right there. Therefore despite reading many posts, as an RST novice I proceeded under the erroneous working assumption that my problem was related to a fault at the last step in the sequence i.e. S84/5 where all progress stopped instead of where the real problem was. Bottom line - take Bobs advice and do a comprehensive check of all the limit switches at the N52 controller. Cheers!
