I have a 89 ranger 2.3 5speed. Ever since I bought the truck 6 months ago it has showed in the low red on the volt gauge. First I thought it was my alternator so I had it checked at advanced auto. They said it was good. When I run my truck my battery shows like 14.6 on the multimeter. And sometimes my truck runs crappy on idle like its going to die. When I run on idle for a period of time(like 5 min) the check engine light comes on. The when I take off the cef shots off a half mile down the road. I can tell if the idle problem and volts showing low can be the same problem. I don't think its the battery because it starts right up everytime. Iv even let it sit for a week. Any suggestions would help

 

Check and clean the other grounds going to the body. The engine ground may be OK but grounds to the body panels and firewall may be rusted.

 

I checked all the grounds I could find. There was 1 on the drivers side panel and one on the firewall. The looked good. I even wiggled them to make sure they weren't loose and they felt tight.

 

A tight connection doesn't mean a good one. It must be a tight clean connection. Corroded connections can be tight but still be a bad connection.