Battery Gague Problem

[MazdaOwner]

Hello, I have a 1996 Mazda B4000 with a 4.0 EFI and I have noticed lately that once the truck has warmed up and the idle drops so does the battery gauge. It drops very low to the point of the headlights start dimming and the fan motor on the inside heater slows down. But, once I start driving, the lights get bright again, and the fan speed goes up too. Does this mean I need a new alternator? Is there some way to confirm that I need a new alternator? Thanks.

 

[chrwilkins30]

the way you text the alternator is to start the truck and take the positive terminal off and if it stays running the alternator is good. Thats the way i learned and every time it shut off i went and got it tested and sure enough the alt. was bad.

 

[AllanD]

the way you text the alternator is to start the truck and take the positive terminal off and if it stays running the alternator is good. Thats the way i learned and every time it shut off i went and got it tested and sure enough the alt. was bad.

That is an excellent way of blowing up the voltage regulator.

Frankly from the symptoms the alternator is already pretty much
certain to be toast...

Probably worn brushes

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[MazdaOwner]

Thank you for the advise. I will look into getting a new alternator for the truck. I just wanted to get some other view points. Thanks again.