Mechanics

CAR WONT START UP & BATTERY DR

1982 Mercedes Benz 300sd

Electrical problem
1982 Mercedes Benz 300sd 6 cyl Two Wheel Drive Automatic 300000 miles

After replacing the Battery, Starter & Alternator in my Mercedes. However once I park the car and try to start it back it will not start. I have to jump the battery every time. The alternator was brand new and I replaced it again.
Something is draining the battery because after getting a jump the car start right up. Any suggestions would be appreciated because my Mercedes Benz technicians are at a loss.
Avatar
Solaire
September 29, 2010.




BATTERY/STARTING/CHARGING SYSTEM TESTING/DIAGNOSIS -1982 Mercede.
BATTERY/STARTING/CHARGING SYSTEM TESTING/DIAGNOSIS
TECHNICAL SERVICE BULLETIN
Reference Number(s): 15/1, Date of Issue: September 1983 Related Ref Number(s): 15/1
ARTICLE BEGINNING
HIGH NUMBER OF UNNECESSARILY REPLACED ALTERNATORS & VOLTAGE REGULATORS
Model(s): All Mercedes Benz Models
Group: Electrical
Bulletin No: 15/1
Date: September 1983
SERVICE INFORMATION
Recent inspections have shown that a high number of alternators and voltage regulators are being replaced unnecessarily. In all such cases, additional components, i.E. Battery, starter, ignition switch or neutral safety switch, are also replaced.
The importance of proper testing and diagnosis of the battery, starting, and charging system cannot be over-emphasized.
To avoid unnecessary replacement of electrical system components, be sure that all technicians are familiar with the following procedures: 1. Battery hydrometer test 2. Battery charging 3. Battery performance test 4. Battery drain tests a. Key " off" drain test b. Key " on" drain test 5. Starting system current draw test 6. Key switch/solenoid circuit test 7. Starter " hot" circuit test 8. Starter " ground" circuit test 9. Charging system tests a. Maximum output test b. Diode/stator test c. Voltage regulator test

WIRING CONTINUITY TESTDisconnect terminal plug from rear of alternator and connect a voltmeter negative terminal to ground. Turn ignition " ON", connect positive lead to each of the connector wires in turn. Voltmeter should read battery voltage as each positive connection is made. If not, trace each wire to find fault. VOLTAGE DROP TEST - GROUND SIDEConnect voltmeter between negative terminal of battery and alternator housing. Start engine and run at approximately 3000 RPM. If voltmeter reading exceeds.25 volt, a high resistance in negative side of charging circuit is indicated. If so, check for loose, dirty or corroded connections. OUTPUT TESTDisconnect terminal plug from rear of alternator and connect ammeter in series between alternator center terminal and corresponding socket in terminal plug. Connect a jumper lead between the " D+" terminal and its corresponding socket in terminal plug. Start engine and run at approximately 3000 RPM. Turn on headlights and leave on for 5 minutes. Ammeter should read maximum alternator amperage at normal operating temperature. REGULATOR CONTROL VOLTAGE TESTAll applicable regulators are designed to maintain from 13.7 to 14.5 volts at a load current of 5 to 7 amps. Alternator should be driven at 4000 RPM and load current set at load current rating. Resistance and speed of alternator may be readjusted if necessary. Read voltage within 1 minute. If not within specifications, regulator requires replacement. NOTE: Test cables should not be removed or load excessively reduced during testing procedure. Considerable load variations may damage the diodes.

BMRFIXIT
Sep 30, 2010.


AD