Have an '06 Ranger 4.0L 4x4. 89k mi. Recently left my lights on and killed the battery. Got a jump and thought nothing of it. Then noticed the fuel gauge was definitely off, as I had just filled up and was reading on low side. Then, I put in park and check engine, oil, and battery lights come on.

Take to auto zone, battery says 100% charged and alternator checks OK (both replaced within 2 yrs). Get home and put in park - engine dies. Recently did have the fuel filter replaced and have been reading about this possibly being an issue.

Could the battery dying somehow relate to the fuel gauge being off/ engine dying when put in park? Or should I focus on fuel filter? Or just some other electrical/wiring/intake to look at?

 

Welcome to the forum

100% charged doesn't mean anything, a bad battery can be 100% charged

get a volt meter

Test battery voltage, key off, after it sits over night, or a few hours at least, 12.3 to 12.8 volts is good battery
12.8volt is new, this is 100% capacity
12.3volt is 5 years old, 60% capacity

Below 12.2volts is a bad battery, may work on warm days but will fail in cold weather

Start engine
battery voltage should now be 14.5 to 14.9volts
After 5 minutes or so battery should show 13.6volts

Turn on all the lights, radio, Fan to HIGH, leave door open
Should still show 13.6volts
Now alternator tests OK


EDIT
Rereading your post, it could be IAC(idle air control) Valve issue
IAC Valve is used by the computer to set idle RPMs
Cold engine should idle at 1,100 RPMs or so
Warmed up engine 750RPM for automatic, 800RPM "in gear", computer bumps it up 50RPM "in gear" or when Air Conditioning is ON

Does the above happen, higher RPMs with cold engine and lower with warm engine?
Just checking if IAC Valve is working