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Old 07-09-2006, 04:23 PM
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Is 15 Volts at Voltmeter Too Much?

I just took the Mustang on a 800 mile road trip, and I noticed an increase in the voltmeter reading as we got further into the trip. The fan fuse popped twice during the trip, and at the trip's end the engine lost all fire - no spark at all. We narrowed that problem down to the magnetic pick-up in the Duraspark distributor. What I'm getting to is that the voltage (per gauge) was reading 15+ volts after I had the fan problem. I'm wondering if that may also have been the cause of the distributor's demise. My understanding is 14.4 volts is max. For most of the trip the voltmeter read just over 14. The alternator is a 100 amp GM type (3-wire) that I modified to fit on the Mustang's 351W.

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Old 07-09-2006, 04:58 PM
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Doc here,

Without reading actual Battery voltage with a known accurate Volt meter (DVOM) you will not know what the output is..

14.4 is max output on a properly adjusted , functioning system..under no load.

On some panel gauges, the accuracy may be lacking..15 volts is close to 14.4..and it may only look like 15 volts.

Measure across the battery with it running , no load, 5 or so minutes after start up, (to replace the surface charge) and it should read between 13.96 and 14.4 volts ...If it's 15 or above..replace the regulator diodes (and the rectifier diodes as well..) Or the whole Alternator..(your choice..$15 bucks for the kit..)

If the diodes are bad...most likely you had raw AC in the Vehicle electrical damaging the electronic componets..(rectifier diodes)

You can get a free test at auto zombie..but Some of those "Guy's" aren't the sharpest crayons in the box..and have been known to "Misread" or screw the test up so check it with a meter first..

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