SL/R129: alarm lock out.. starter lock out wont turn over all lights on
Thread Starter
Newbie
Joined: Jun 2017
Posts: 2
Likes: 0
1992 Mercedes Benz 500 SL
alarm lock out.. starter lock out wont turn over all lights on
1992 SL500 was the perfect car.. I love it.. but replaced battery in key fob (one button) and seem to work.. got in minor fender bender got it fixed..mechanic said it would not turn over.. so he left key on seat? next day started and ran just fine.. after that it will not turn over.. all lights on dash board come on, can hear fuel pump etc turn key all the way and nothing.?? checked voltage at starter and it showed major drop so I replaced the starter.. tried again wont turn over with key.. but could jump it and it would run... any ideas on this... I tried talking to a service person at the dealership and I dont think he could spell Mercedes LOL.. please help.. how do i reset this whole thing or what to check next.. it only has 78K and was always kept inside.. thanks
Banned
Joined: Jan 2006
Posts: 1,982
Likes: 393
From: Atlanta, unfortunately
'09 S600, (2) R129 300SLs, '03 SL500, '03 SL55
A U.S. '92 car has no alarm lockout, and the circuit is simple: battery --> ignition switch --> neutral-safety switch --> starter solenoid. A logical place to begin troubleshooting is at the X26/12 connector (picture). Removing the radio and/or ash tray may give all the necessary access required.
The neutral-safety switch is wired to the male half of the connector with purple and white-striped wires. To check the switch separate the connector and measure resistance between the pins associated with the switch. With the gear selector in "P" or "N" there should be a short circuit, naturally.
If the neutral-safety switch is okay, then the ignition switch is suspect. To check that you measure voltage between the purple wire at X26/12 and chassis ground while the connector is partially separated -- separated enough to probe the voltage but not so far as too lose electrical contact. With the key in position 3 (start), if the ignition switch is good there should be 12VDC.
The neutral-safety switch is wired to the male half of the connector with purple and white-striped wires. To check the switch separate the connector and measure resistance between the pins associated with the switch. With the gear selector in "P" or "N" there should be a short circuit, naturally.
If the neutral-safety switch is okay, then the ignition switch is suspect. To check that you measure voltage between the purple wire at X26/12 and chassis ground while the connector is partially separated -- separated enough to probe the voltage but not so far as too lose electrical contact. With the key in position 3 (start), if the ignition switch is good there should be 12VDC.
