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Virtual Wrench, Ford Mechanic
Category: Ford
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Experience:  35 years Master Mechanic
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Ford F150: 1998 Ford F150 - Problem(s) - Noted Volt

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1998 Ford F150 -

Problem(s) -

Noted Volt Gauge, in the dash mounted instrument cluster, would jump from indicating Zero to about 12+ volts when turn ignition key to the accessory position with engine not running. Volt gauge continued reading the 12+ volts with the engine running (no change).

Later the Batt (went dead) would not crank/start the engine.

Attempted Corrections -

Replaced old Batt with New Batt correct for vehicle and Cleaned Batt Pos/Neg cable connector ends.

Replaced the existing Alternator with New 300 amp unit and replaced the 103" Serpentine Belt.

Results -

The engine will most certainly crank and start. However, the dash cluster Volt Meter continues to behave the same - Key Off postion = reads Zero Volts. With Key to the accessory postion (with engine off) volt meter reads/jumps to about 12+ volts. When Start the engine/engine running the volt meter continues to read about 12+ volts with No Change when electrical loads are applied and or changes in engine RPM.

Any Ideas?


Thanks for the very detailed information. If there is 12 volts to the batt wire on the back of the alternator, and the fuses are good, then Every single thing you mentioned points directly at the alternator not charging. If it was charging, it would read 14.5 volts with the engine running at high idle with or without any accessories on. A 12 volt system requires 14 volts to be charged. It will need replaced. I know you mentioned t has been replaced but i have seen many, many rebuilts fail right out of the box.


Check over the wiring real good. See below.

If you have further questions feel free to reply.


Hi john,

Sorry but that was the wrong diagram. Here is the correct one.
Customer: replied 3 years ago.

Okay - I'll get another alternator

Thanks and Best Regards XXXXX XXXXX

Hi John,

Yes do. I'm sure that is the problem.
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