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Old 12-21-2009, 08:58 PM
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Voltage Drop

My 1990 Wrangler with a straight six and 5 speed has developed a mysterious problem. When it starts from cold, voltage on voltmeter shows about 14 volts. After driving for about 20 minutes, indicated voltage drops to about 6-8 volts. However, measuring voltage from alternator (output bolt to negative battery terminal) still shows about 13.5 volts. Alternator was bench tested at autoparts store, they say it's OK. Belts, connections seem tight. I have cleaned battery terminals, but this is the second battery it has eaten. Some guy said maybe my fusible link is going bad. Unfortunately, I don't know where that thing is, or what it looks like. Anybody out there have any ideas? Thanks.
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Old 12-21-2009, 09:06 PM   #2
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I think the ammeter is registering the battery voltage and the alternator doesn't always kick in to charge. However, I have had a smilar problem on my '87 wrangler and the problem was in the gauge. They aren't real robust. Sometimes, mine acts fine, other times the needle is all over the place. I replaced the connectors to the battery, checked the alternator and then took it to an electric shop who determined that the gauge is funky. Good luck.

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Old 12-21-2009, 10:20 PM   #3
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this could be heat related. as heat increases effeciency decreases. i would start by making sure the alternator is clean, inside and out. the short run at the auto store is not enough to cause a thermal breakdown.

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Old 12-22-2009, 10:11 AM   #4
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X2 with Navy Chief. Sounds like your alternator is going bad. The key is that you went through 2 batteries. My alternator tested o'k also. However, my gauge was all over the place. Replaced the alternator and the gauge is perfect and no problems. I found that with bench tests, it's only an indicator. Think of it this way, how many jeeps that run with an alternator being bench tested come up bad. Usually it goes bad and then you either hear bearing noise or your battery goes dead due to lack of charging. I would charge the battery and make sure it holds the charge. If it does I would replace the alternator.
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charging , fusible link , voltage drop

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