Cadillac Repair: lights osolating, negative battery cable, digital voltmeter

Question
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Followup To
Question -
Thanks Bill, The problem exists all the time while driving or at idle. The alternator reads out 13.9 to 14.8 on the inst panel. I put meter on bat and voltages fluxuate from 14.4 to 14.8 while ideling. I'm not sure if this is an elec problem or alternator.

Thanks again, Randy

Answer
Hi Randy, It does sound like the alternator could be on the way out and need replaceing. If you take a digital voltmeter and place it across the battery bolts and the readings are the same, fluctuate between 13.9-14.8, then with the engine running and all the accessories on that you would normally use place the neg lead on the battery neg bolt and touch the pos. lead to a good clean metal surface on the engine. If your reading is higher than .2 volts then you have a ground problem like the negative battery cable is dirty or too high a resistance, the cable that attaches to the engine is loose or the metal under the cable end is dirty. You could also have the same problem on the positive cable and its attaching point on the alt. Place the pos. lead on the B+ cable bolt at the battery and the neg lead on the B+ alternator bolt and again see that the reading is less than .2 volts. Make sure that you don't touch metal and the alt. bolt at the same time or you will see sparks and could damage the alternator if it isn't already. If it is less than .2 volts then you should have the battery and alternator tested at a shop to determine if the problem is a battery, voltage regulator inside the alt. or weak diodes inside the alternator which would require that the alternator be replaced. Hope that helps. Bill