I have a 1994 V 940 and the battery doesn't hold a charge once the car has been running. At no time does the generator light on the dash come on. Have tried replacing both generator and battery with new. Absolutely baffled. Does anyone have any experience with this

 

First when you start the car with key in position 2,the battery light on the dashboard must light on before the car starts,otherwise your battery will not get charged by the generator.Check that out first.It is possible your battery light on the dashboard is out.If that is ok then check the fan belts so they are rightly tight.It is also possible that the battery or generator is faulty even if its new.You can start the car and check the voltage on the battery with a voltmeter and it should show around 14 on the scale so you know it charges when on.

 

Fixed it! The problem was a bad diode between wire C:16 going to the instrument cluster from the generator and the generator light (number 14). Got a new 1N4004 diode at Radio Shack for $1.65, soldered it in and viola - car is charging perfectly now.

 

Hi my 1994 940 is doing the same thing that yours was last year. How did you know it was the diode? Did you soldered it in on the back of cluster by the number 14 lamp? Any help is greatly appreciated.

 

before tearing into the instrument panel, do some basic tests.

fully charge your battery overnight with a battery charger, disconnect the charger, wait at least an hour. measure the voltage at the battery, it should be about 12.6V give or take a few 10ths. if not, then your battery is likely bad (or your charger is no good?).

if the battery is OK, turn the ignition on (without starting car), does the alternator light come on? if not, then the bulb and/or wiring is bad. if it does come on, when you start the car, does the alternator light go out? if not, then maybe the alternator is bad.

if the light goes out after starting, measure the voltage across the battery with the engine running, it should be about 1.2V higher than the voltage with the car turned off, and if it is, then your alternator is working fine, maybe your battery is bad after all (the above voltage test is not definitive).

if the alternator light comes on, but won't go off after starting, stop the engine, turn ignition on (without starting car), use a volt meter and verify that there is 12V at the D+ terminal (smaller red wire) on the back of the alternator relative to ground. if not, then the alternator won't work.