Question about 1991 Volvo 940
OK the battery in good charge should be at 12.5 volts ( as measured with a voltmeter across the terminals) When the engine is running you should expect the reading to be about 14 volts. Put the lights on ( a load on the battery) and the voltage can go as high as 14.5v. Switch everything off (I mean everything..radio etc) and disconnect the negative terminal to the battery. Now put the meter in ammeter mode and measure the current between the negative terminal and the cable that is now disconnected. It should be really very low current (milliamps at most), switch on the lights to show ourself what that current drain looks like. If the residual current looks significant take out each fuse in turn and return it noting on pen and paper any drop in current when the fuse is out. This process will identify the circuit that is draining the battery. Check the wires and junctions in this circuit for shorts etc. If its lights try removing bulbs until the current drain stops If possible leave the fuse out over night on this circuit and see if this effects the battery's ability to charge and stay charged.
Posted on Aug 30, 2010
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Posted on Jan 02, 2017
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