Im having a problem with my 2000 ford ranger 2.5l manual... my alternator only charges sometimes... when the alternator is in the no-charge state the green/red wire only measures 1.34v... it does this off and on while the truck is running... shouldnt this always read 12v when the key is on run or start? or is this the out put signal to the batt light?... please some one help me... ive been at it for two days and i cant figure it out

 

Take the Alternator off and see if the pulley has any resistance, see if you can hear anything inside abnormal sounds etc.

 

Connectora are probbly worn within the alternator. Replace with new or find someone tht will rebuild it

 

Measure voltage at the battery.

 

I have measured at the battery and confirmed it is intermittently charging... Like I said in the first post... The only thing I notice that is out of the ordinary while it's not charging aside from the fact that it is only reading 12.4 volts at the battery, is that it is Only reading 1.34v at the I terminal (green/red wire)... Why would this be?

 

I don't have the manual handy but is that the single wire on the small connector? If it is that is the feed wire for the light and volt meter on the dash.


Power is comes into the alt on the other connector.

Also measure AC voltage at the battery.

 

It is the wire that leads to the battery light that is supposed to be the energizing wire from what I've read

 

The Light Green with Red Stripe wire goes to the warning indicator lamp in the dash.

With the ignition in the run position (engine not running) does the indicator lamp come on? If not, disconnect this wire at the alternator and ground it. Does the light now come on?

For a basic wiring diagram of charging system Click this link Charging Ststem

 

You should still pull the alt to make sure its not at fault. If the regulator goes bad it will ground that wire at the alt turning on the light. If you have a partial failure it may not light the lamp but it will still not charge.

 

Yes it does come on when I turn key on engine off

 

The following is a synopsis of the circuit operation:

With the ignition in the on position, voltage is applied through the warning indicator I circuit (Light Green with Red stripe wire pin 3 of the connector) to the voltage regulator. This turns the regulator on, allowing current to flow from battery sense A circuit (Yellow with White stripe wire pin 1 of the connector) to the generator field coil. When the engine is started, the generator begins to generate current. This current is then supplied to the vehicle’s electrical system through the output B+ terminal.

Once the generator begins generating current, a voltage signal is taken from the generator stator and fed back to the internal regulator. This voltage feedback signal (typically half the battery voltage) is used to turn off the warning indicator.

Checking system operation:

Using a DVM back probe connector with it plugged in to the generator. The voltage readings should be as follows:

Key on-engine off:
Pin 1 12 volts (Yellow with White stripe wire)
Pin 3 1-3 volts (Light Green with Red stripe wire)

Key on-engine on:
Pin 1 12 volts (Yellow with White stripe wire)
Pin 2 12 volts (Light Green with Red stripe wire)

If the readings are out of spec you have two options, one is to check the commutator rings. If there in fair condition, you could try replacing the voltage regulator and brush set. The other is replacing the alternator.

Here are a few links that may be of some help:


Video 2

 

https://www.ranger-forums.com/showth...hlight=brushes

A How-to for Ranger alt brush replacement.

 

Thanks guys that helps a lot... So these symptoms are consistent with brushes being worn?

 

Have you have the alternator tested by an auto shop that can do a load test ?

Also, if the alt tests OK check out the grounds in the engine bay, (battery to frame, frame to engine, frame.engine to body) add one from the body of the alternator to either the engine or the frame ground location. Also chk the engine to body ground.
Make sure all have good clean connections.

luck

 

Thanks guys... Pulled the regulator and the brushes and rings looked terrible... Parts store had one in stock so I just replaced the whole thing... So far so good... I'm gonna keep an eye on it though... Y'all are a huge help... Look forward to getting this truck closer to my goal with this forums help