Sooooo my 99 ford ranger v6 3.0 was in a rollover incident about a month ago, when I was able to start working on it a couple weeks ago I found the battery was frozen and it wouldn’t hold charge. So I thawed it out and tried again, it fired right up but battery gauge was still reading low and battery light was on. I tried bringing it on a drive for a mile at 50mph to make sure everything was good and when I did noticed that there was no air blowing out of my vents when I turned on heat and also lights were starting to dim. Put on my blinker and the gauges started going wonky, first rpm went off the charts up and down then when I tried my blinker again my abs light came on and shortly after it died, had enough juice to barely get it off the road but every time I hit the gas pedal it would shut down further. My initial thought was alternator seeing as battery was checked and deemed good, however I got the alternator tested on and off the vehicle and NAPA said it was good, so I’m pretty baffled. I had heard that it could be an issue with the computer although am not sure where to start, any help would be greatly appreciated

 

Welcome to the forum

Not a computer issue.........for sure

Battery voltage(key off) should be between 12.3v and 12.8volt
12.8v is a new battery
12.5v is a 3 year old battery
12.3 v is a 5/6 year old battery and time to shop for battery sales
12.2v or lower is the done battery, it WILL let you down

Start engine
Battery voltage should now read above 14volts but under 15volts, alternator is working

If you still see 12volts then its NOT working
In engine bay check ALT SYS FUSE, 30amp
In cab fuse box check Fuse 15, 7.5amp

If both fuses TEST OK, then there is a wiring or alternator issue

Key off
Put Volt meters black probe on Alternators metal case, for all tests
Touch Red probe to B+ terminal, on back of alternator, it is a stud/nut terminal, should see Battery Voltage, if not MEGA FUSE is blown, 175amp, its on the outside edge of engine fuse box

Unplug the 3 wire connector on alternator
Test the Yellow wire, should see battery volts, if not 30amp ALT SYS fuse is blown
Test Light green wire, should be 0 volts
Turn on the key, engine OFF, re-test Green wire, should see battery volts, if not Fuse 15 in cab is blown
Make sure the short white jumper wire is plugged in to its single tap slot on the back of alternator

Start engine
If all 3 wires test as OK, and battery volts are not above 14volt with engine running then alternator is BAD, regardless of other tests, B A D