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124 300CE European Model
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Discussion Starter #1
I am having an electrical nightmare that is driving me crazy and I am looking for some help to find a resolution(s). Here are the facts and problems when I got the car:
1. 1988 300CE, Japan Model purchase 2 years ago with several problems
a.Mint body with no rust anywhere
b Dual Climate control – max heat on passenger side & no heat control on the driver’s side but the AC Compressor was charged and cycled on and off when the AC button was pushed on. Sometimes there would be no power to the 3 buttons between the Air flow and fan speed selector knobs
c.Rough, high & surging idle
d.Cold start problem
e.The console and dash had been apart at least once prior to my purchase
f.There is a replacement Pioneer Stereo in the car
g.The rear passenger side window would not work and the relay was warm to the touch
h.Exterior Lamp Failure light in gauge cluster would light up when the break was applied but no light is burnt out
i.Gas leak on the Electric/Hydraulic control located on the throttle body.
j.Rough shifting into reverse (common problem)
h. Most of the rubber seems to be worn or srunk

Here is a chronological list of my attempts to fix the car over the past 2 years

2. Did a complete tune up with MB parts and replace the front and rear struts
3. Replace the Duo Valve with a used one reported to be checked prior to sale, had the Climate Control Module rebuilt, replaced the air flow directional selector with a used one and the vacuum control module located on the side of the heater control box – no change, the same problem remained.

4. Replace the Idle Control Valve & Electric/Hydraulic units which improve the rough idle, stopped the surging. The cold start problem has improved but still a problem. Replaced the, OVP, Kilma, Window (It was getting warm) & Kickdown relays. Also replaced the Exterior Lamp Failure Module. The exterior Lamp Failure light stills comes on when the brake pedal is applied and the idle is OK but not as smooth as it should be. The replacement window relay - still got warm. The car seems to miss once and a while and still can run up on the idle now and then.

5. Replaced the Window Relay and rear passenger side window switch. The window would go up and down but only using the center console button. Changed both switches and then only the rear switch would work.

6. Sent the car over to a local shop specializing in MB repairs asking them to find the climate control problem and fix it. They had the car for 10 months. They removed and rebuilt the heater box and returned it to me with the same problem and numerous more that are not related this forum. The oil pressure gauge and tach quit within hours of leaving the shop and the rear head rests would not stay up.

7. Tested all the electrical and vacuum lines - replaced several rubber vacuum connections. The heater box vacuum seems to be working as it should.

8. Sent the car to MB to have them diagnose the climate control problem. I was advised the Climate Control module, duo valve and tranny kickdown switch were bad. The Mechanic also advised the climate control problem could be by-passed once a replacement duo valve was installed. Disconnect the control wire going to the passenger side of the duo valve . Then run a jumper wire from the driver’s side control wire to the passenger side. Simple right, but, I never had a chance to check for resolution because once jumper set up was plugged in the #12 fuse (Blower Motor) melted through the fuse panel.

9. Removed and cleaned all ground connections in the engine compartment and behind the gage cluster. They were super clean but a rubbed them with emery cloth to be sure

10. Replaced the fuse panel and installed all new copper fuses. Number 12 fuse would heat up enough to burn my finger when the fan was turned on so I removed the fuse

a. Now none of the windows will work and the window relay seems to be a little warmer than before. I changed it out a couple of times but the windows will not work.
b. Under the rear driver’s passenger seat are 2 vacuum/electric switches. The rear head rest switch leaks vacuum and the switch beside it is hot to the touch. I can hear it snap when the plug is push on the connectors.


Any ideas on what might be my problem(s)? Am I dealing with a number of separate unrelated problems or are these related somehow. I am ok with most repairs and will tackle almost anything. Anything but electrical that is. I know nothing about it thus my nightmare.

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