When I turn the key on I have no power, it builds and starts. What do I check. on 1994 Mazda B2300

When I first turn on the key on my 1994 Mazda B2300 I have no power. The charge slowly builds to virtually full in about 30 seconds. Once running the voltage meter bounces considerably, but the truck runs without any problems( Until I shut it of and all power is lost immediately.) Do you know where I should start in checking things out?

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1 answer 1 comment
I would suggest you begin by checking the battery and its connections. The battery should be load tested and be sure the connections are clean and tight.
Thank you Jim,

I was able to test the battery which was giving off a widely fluctuating charge. I appreciate your help.