. Set idle rpm to specification.
. Clean battery terminal and cable connections. Check the condition of the battery cables, especially the ground cable. Look for unseen corrosion under the insulation. Clean the main ground, where it bolts to the chassis, and apply dielectric grease.
. Remove and fully charge the battery. Most auto parts stores will do this for free.
. Test all under hood and under dash fuses with a test light or multimeter:
https://www.askmehelpdesk.com/cars-t...tml#post252145
Be very thorough, since it could save a lot of time and money.
. Clean the connections of the wire going from the alternator to the under hood fuse box, after disconnecting the negative battery cable.
. Test the battery voltage and the regulated battery voltage, as explained in the link below:
https://www.askmehelpdesk.com/cars-t...ml#post1973613
This work-up should indicate where the problem resides.