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Billy
Billy, Trainer/Master tech.
Category: Mercedes
Satisfied Customers: 3498
Experience:  Trainer 8+ years, Master tech. 10+ years, SAE member
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420 sel: 1990 Mercedes 420sel the overload relay gets hot and

Customer Question

1990 Mercedes 420sel the overload relay gets hot and the car will not start relay is a year old how to fix ?
Submitted: 1 year ago.
Category: Mercedes
Expert:  Billy replied 1 year ago.
Hello and Welcome! I'm Billy and i will assist you with your inquiry. Feel free to ask if any further info is needed.
Is the the overvoltage protection relay?? under the windshield, towards driver's side in engine bay plenum?
Customer: replied 1 year ago.
yes it is and a red top.
Expert:  Billy replied 1 year ago.
Hello,
The overvoltage protection relay prevents damage to the CIS-E control unit from excessive voltage which may occur when vehicle components are
switched on and off or in the event of an overcharge to the vehicle battery.
Accordingly, i would first check the alternator output. It should not exceed 14.5 volts even at 3000 rpm.
If the problem persists, i would further check as following:
https://drive.google.com/file/d/0B6Zgf4dbmODzRHVGOEhpRDUzOWs/view?usp=sharing
Kindly get back to me with your findings, or if further assistance is needed.
Regards,
Billy

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