Mysterious Electrical Gremlin in 300e
 

I finally got my 1993 300e 2.8L running after I got a new OVP relay and decided to take it for a test drive. The car ran excellent and I thought that I was Large and In Charge, however, just then it shut off. No power anything. No power to sunroof, windows,etc. I realized that the battery must have been drained and it was. I walked two miles home(didn't take cell phone) and got another battery and put it in the car. It started right up and I immediately drove it back home. When I got home the alternator was smoking and I knew it was fried. So I know I need to get an alternator, however, another problem arose. I left the charged battery in overnight with the alternator out and the next morning the battery was drained. So I charged up the battery and put it back in the car. When I connect it, I get a buzzing noise like the doors are open and then it stops. I think that may be normal, but then there is a buzzing noise coming from the drivers side of the motor, just under or around the throttle body. Is this normal? It continues as long as I have the battery connected. I believe this is what drained my battery overnight after removing the alternator. I plan on testing the circuits when I get time. If anyone has any input, it would be greatly appreciated.

What color OVP did you use??

Hi Daddi,
Thank you for your help on my last problem(300e won't shut off). I had a OVP that would not allow my car to shut off. It was part# 201 540 32 45. I replaced it with OVP part# 000 540 67 45 and the car started and shut off fine. The car came with the OVP part# 000 540 67 45 when I got it(not sure if it was the OVP that belonged in the car) and I originally ordered the wrong one. The car ran fine until the battery drained down and I lost all power. Is the buzzing noise that comes from the drivers side of the engine supposed to do that? If I knew what could be buzzing, maybe I can track down the circuit and check it out. The car is an ongoing project and I have other vehicles to run so I only work on it when I get free time. Any help you can give me will deeply be appreciated.

Hello again Daddi,
I did a little troubleshooting this morning. I connected the battery and I began removing fuses to see what controlled that buzzing noise around the throttle body. When I removed the No. 7 fuse the buzzing noise changed to a ticking noise, almost like a clock but faint. According to the fuse box diagram, #7 fuse controls: back-up lamp, heating water valve, water pump, engine fan, Heating system for washer jets, climate control system, relay auxiliary fan term.86, aut. transmission electrics, air condition compressor. If I remove all the fuses the ticking is still there. Sounds to me that the faint ticking noise is also my electrical gremlin. What do you think? Should I wait and install the alternator before going further? I'm wondering if the alternator must be connected to troubleshoot the electrical system. Maybe that ticking has to do with the heating water valve or heating system for washer jets. Please let me know your thoughts......Thank you in advance

The buzzing you hear is coming from the throttle body, the throttle body is powered by the OVP. Your car should have either A 000 540 67 45 or A 000 540 52 45 OVP both have white tops. If you use OVP with red top the throttle body does not power off and drains your battery.

Hi Daddi,
Sorry for the delayed response. You were right, again. After reading your reply, I realized that when I was stranded and the battery was drained, in desperation I switched out the new OVP for the old OVP to see if that would make a change. I had the old OVP 201 540 32 45 (black top) in when I was getting the buzzing noise. So I put the new OVP that belongs in there, the 000 540 67 45(white top) and the buzzing noise is no longer present. However, I still have some type of short somewhere. After reconnecting the battery, I had 12.46 volts at the battery. Approximately two hours later it was down to 12.11 volts. I guess my next move is to start tracing the circuits in an attempt to find the short. I am also going to clean all the ground points. When I finally track it down, I will post the results. Once again, you helped me. You really know your Mercedes. Thank you.

Thank you.

25 years of fixing them teaches you one or two things. How old is your battery?

The battery that I am currently using is about two years old and it is from another one of my cars. I didn't want to put a new battery in until I find the short since it would be drained overnight. Let me know your thoughts....

Have you measured if it is drawing amps??

I have seen new batteries die after going flat.