I’ve got a 2003 4.0L Ranger and there’s something strange happening.

When I get over 2.5 or 3 rpm my battery light in the dash comes on, battery power gauge needle dips towards low.
When rpms go back down towards 2, battery light turns off and gauge needle goes back to where it’s supposed to be.
Battery was replaced about 6 weeks ago.

I’ve never seen this before. What might be the issue here?

 

Most likely the alternator is bad, its shutting off at higher RPMs

Battery light means the vehicle is getting ALL its electrical power from the Battery
Like when you first turn on the key, Battery light is on and all the lights, radio, heater fan are ALL running off the battery voltage

When you start the engine, and alternator is working, ALL electrical power comes from the alternator, NO power comes from the battery, battery is only there to start the engine
So when Battery Light comes on it means................Battery is being drained, and if engine is running it also means alternator is NOT working

 

Gonna share a DUH IDIOT Moment. My Battery light came on (mines a 2.5 lima btw so don't take this as a factual guide for yours). I immediately took out the multimeter and started testing.
Voltage was jumpy but within spec coming off the alternator(13-14)
Battery was a little lower than I like but within spec as well (12.5).
My in dash voltage gauge would just pick and choose whenever it pleased to go just a little below midway. No real correlation with gassing it or slowing down etc.

Finally got pissed and decided I was gonna Yoink the alternator out. 30 seconds into yoinking I found my issue

Helps when everything is plugged in

You know when everyone asks "did you check all your wires?" And you think to yourself "yeah what do I look like? You think I'm Stupid or something?" Check your wires lol.

If wires are good I'd suspect a bad voltage regulator.

 

[QUOTE=Slow;2197735]Gonna share a DUH IDIOT Moment. My Battery light came on (mines a 2.5 lima btw so don't take this as a factual guide for yours). I immediately took out the multimeter and started testing. Voltage was jumpy but within spec coming off the alternator(13-14). Battery was a little lower than I like but within spec as well (12.5). My in dash voltage gauge would just pick and choose whenever it pleased to go just a little below midway. No real correlation with gassing it or slowing down etc. Finally got pissed and decided I was gonna Yoink the alternator out. 30 seconds into yoinking I found my issue. Helps when everything is plugged in. You know when everyone asks "did you check all your wires?" And you think to yourself "yeah what do I look like? You think I'm Stupid or something?" Check your wires lol. If wires are good I'd suspect a bad voltage regulator./QUOTE]

^+++ LaughingOutLoud\LOL
Yep,
1st rule of electrical troubleshooting: "Is it plugged in?"
2nd rule of electrical troubleshooting: "What got worked on last?"

 

Had the alternator tested. It passed. Got a new connector. Is it possible that it needs a new regulator? Other ideas?


A little corrosion on there.

Doesn't look terrible, passed the tests. Regulator issue?

 

Alternators can not be tested except in the vehicle, just FYI
Wish they could be
All they can test is if the alternator generates more than 13volts, which you already knew it could because battery light goes off after start up

Connector shows corrosion on one terminal, clean it up, not you problem but will be one day

Sure, you can replace just the voltage regulator, more than likely that's the issue but since higher RPM is the issue there could be a "wobble" on the rotor so voltage regulator wouldn't help

 

Regulator brushes look okay, pretty springy.

New connector on, still waiting for the exciter wire connector, which is $7 on Amazon, $40 at O'Reilly's. Wtf?

 

Hey y'all.
Just wanna say thanks for weighing in on this alternator issue. I appreciate it. I'm getting ready to head across the country in this truck and needed this fixed ASAP. Put a 95 amp alt in (old one was 130 amp) and my battery light issue is gone. I don't know if it was just the regulator or actually the alternator. Don't even care. A couple more smaller projects and I'll be hitting the open road.
Cheers!