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Old 06-19-2017, 10:29 PM   #1
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VanDiemen23's Avatar
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Odd electrical problem

I have a Cat 3126E in a 99 Beaver. Coming home today the voltage gauge suddenly dropped from 12 to below 10, and the trip computer re-set. Tach went crazy too. Got out the meter and with all major electrical off, both coach and chases batteries were over 13V. Turn on the lights, wipers, or AC and it dropped to 10-ish.

No obvious problems from the trans or engine ECUs, although at one point the trans display got pretty dim.

Found the positives on one of the chassis batteries and one of the coach batteries were slightly loose, but tightening them made no difference.

Wipers were most affected, as they would freeze in mid stroke until the power came up to 12 again, and as soon as they started to move it would drop back to 10. took more than an hour for them to return to the park position.

On the switch from 12 to 10 and back it was abrupt, like a relay switching. Eventually it stayed at 10. Had a harrowing last 40 minutes back to home in the dark, with my wife driving the toad in front for guidance and safety and me with no lights other than the markers. I was worried that if the voltage dropped too low the engine electronics would abruptly stop working and leave us stranded someplace with no shoulder.

Anybody run into this before? Alternator or voltage regulator failure?

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Old 06-19-2017, 10:40 PM   #2
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Location: Pensacola, FL
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May be a poor connection in either the power or the ground side. Best to do a voltage drop test on both while the symptoms are present.

Google will give you lots of links if you are not familiar with this basic test.

One example here:


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Old 06-20-2017, 10:31 AM   #3
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I think it's the alternator
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Old 06-20-2017, 09:16 PM   #4
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If you can get under it, check the battery cables at the starter. It sounds like one of them may be loose.
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