Replace the battery, and most likely, replace the generator again. You're way ahead in testing compared to what most people know to do, but you have to understand that since these were redesigned for the '87 model year, GM's generators went from one of the better designs in the world to by far the worst. Due to their design, they develop huge voltage spikes that can destroy the internal diodes and voltage regulator, and interfere with computer sensor signals. The battery is the key component in damping and absorbing those harmful spikes, but as they age and the lead flakes off the plates, they lose their ability to do that.
I'll be back in a minute with part 2.
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Monday, June 29th, 2020 AT 6:55 PM