[Mr. Farknocker]

I've been experiencing battery drain problems with my 92 300SE while the vehicle is not being operated. I thought it was a short that caused the battery to drain. On occassion, I'd see red/blue lights on the center A/C vents light up and thought that it must be because of a short in the electrical system after the car is turned off.

I recently noticed that the "REST" button on my 92 300 SE's a/c control panel lights up after the ignition is turned off. This seems to fire up the defrost fans and results in a drained battery. Does anybody know what the problem is and how to solve it?

TIA

 

[Mr. Farknocker]

Re: This turning on itself is a sign of electrical gremlins. I suspect that the battery is on

Originally, I thought it was the battery (a 2 year old Benz batt that was exactly 2 yrs old) so I swapped it out for another 64 month battery. Granted, it wasn't a Benz battery but it was working in another vehicle and was fully charged with a battery charger before installation. It was drained in a matter of hours after installation into the Benz and could not muster enough energy to turn the motor over. This leads me to believe that something was draning the battery after the car was turned off.

I think you're on to something about the low voltage and electrical gremlins, though. This is the first time I've seen the REST button light go on. On other occassions, I've seen the red and blue lights on the center A/C vents turn on. BTW, once the REST button goes on, I can't seem to turn it off. I'll try your recommendations and report back here.

This turning on itself is a sign of electrical gremlins. I suspect that the battery is on its way out and the voltage pulses used by the CC system are being violated.

Connect your battery to jump leads and a donor battery and then start your car. Kill the ignition while still attached to the donor battery and see whether REST kicks in itself. My guess is that it wont while connected to the donor battery. This is a sign that yours is on its way out. Take the battery to a check centre and have it diagnosed. Even one dead cell of the six will cause ignition faults as you describe.

 

[Mr. Farknocker]

Re: REST Button

How can I tell which chassis I have?

IT applies to Chassis #A055784 to A078197

 

[Mr. Farknocker]

Re: This is known problem with early 92 W140 cars. You need to check software status on the

This is known problem with early 92 W140 cars. You need to check software status on the pushbutton controller. To check software status push and hold REST button until you see "1" on the left LCD window. Push left AUTO button until you'll get "9" in this window. Right LCD will give you software status. If it is 62 you need to replace pushbutton controller. Another reference is a production date of the push button controller from 3/92 to 9/92

I checked the status and it showed a "62". I guess this means that the pushbotton needs to be changed. How difficult is it to replace the pushbutton? I'd like to do it myself if possible.