• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

Battery light on


dvdswan

Well-Known Member
U.S. Military - Veteran
Joined
Feb 11, 2021
Messages
1,115
Reaction score
572
Points
113
Location
Seattle, WA
Vehicle Year
1991
Make / Model
Ranger XLT 2WD
Engine Type
3.0 V6
Transmission
Automatic
2WD / 4WD
2WD
My credo
Keep your mind like an umbrella, it only works if its open... Continually learning.
The Battery light came on today. Everything seems normal. 91 3.0L 2wd auto. I checked the battery voltages:

key off - 12.65 vdc
key on/engine off - 11.94 vdc
key on/engine on - 14.65 vdc

I'm stuck and could use some help. It seems normal, is it possible that the alt connector is making a bad connection? or the battery light connection is bad? Belt is not loose or squealing.

I changed the oil yesterday and son drove it so I don't know if it did anything to the connectors on the alt. They do look normal.
 


Rock Auto 5% Discount Code: 70D65189E6D8FF: January 5th, 2022

dvdswan

Well-Known Member
U.S. Military - Veteran
Joined
Feb 11, 2021
Messages
1,115
Reaction score
572
Points
113
Location
Seattle, WA
Vehicle Year
1991
Make / Model
Ranger XLT 2WD
Engine Type
3.0 V6
Transmission
Automatic
2WD / 4WD
2WD
My credo
Keep your mind like an umbrella, it only works if its open... Continually learning.
Had the battery and alt tested at the local auto parts store. Both were good...

Checked the belt which was good and tight. Even tightened a little bit more. No changes.

How can I tell if the alternator has an external or internal regulator?
 

RonD

Well-Known Member
Joined
Jun 2, 2012
Messages
20,413
Reaction score
4,100
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
1991 Ranger

Look at alternator, if you see a 3 wire connector on the top/back it has internal regulator

The light green/red stripe wire on this 3 wire connector is the Battery Light wire

The way it works is that the Battery light bulb in the dash gets 12volts with Key on
The light green wire is the GROUND wire for the bulb
When key is on and alternator is off, the green wire is a Ground, so battery light is ON
When you start the engine the alternator should generate voltage, so green wire is no longer a Ground and battery light goes off

Unplug the 3 wire connector
Turn on the key
Battery light should NOT come on, because green wire is not grounded anymore
If battery light comes on then green wire has a short to a ground somewhere

If battery light is off then green wire is OK
Make sure Short white jumper wire on the 3 wire connector is plugged in, it plugs into a single spade terminal near the 3 wire connection on back of alternator

Plug 3 wire connector back in
Start engine
If battery light stays on then voltage regulator is most likely failing

The POINT of a voltage regulator is so you don't "cook" your battery or the electronics in a vehicle
The fact an alternator generates 14volts means the rotor part of alternator works, which is good, but not the whole story
Alternators needs to be restricted to under 15volts, and under 14volts after about 5 minutes of re-charging
And that's what the voltage regulator is there for, its a Limiter, a "regulator", lol

A 12v battery should be 12.3v to 12.8v, key off, under 12.3v means battery is failing
Your posted DROP from 12.6v to 11.9v with key on means there is an electrical issue, that's a BIG Drop with key on, maybe Fan was on HIGH, big audio AMP or auto headlights came on?

Anyway after start up test battery voltage, 14.6 was fine but REV engine to 2,000-2,500rpm and hold it there
See what voltage is, should be UNDER 15v
If it goes higher then regulator is bad and that's why battery light is on
 
Last edited:

dvdswan

Well-Known Member
U.S. Military - Veteran
Joined
Feb 11, 2021
Messages
1,115
Reaction score
572
Points
113
Location
Seattle, WA
Vehicle Year
1991
Make / Model
Ranger XLT 2WD
Engine Type
3.0 V6
Transmission
Automatic
2WD / 4WD
2WD
My credo
Keep your mind like an umbrella, it only works if its open... Continually learning.
@RonD Thank you. I will work on it tomorrow morning.

BTW, I did have the fan on med or hi. lol
 


Top