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Truck Won't Charge

Having trouble with my truck not charging. Changed out alternator, v/r and battery and still will not charge.Thanks

Does the alternator light in the dash work? If the bulb is burned out, the alternator won’t charge the battery.

What condition is the accessory drive belt?

Good tension?

All fusible links and fuses for the charging system good?

Start the engine, and bring the idle speed up to 2,000 RPM’s for thirty seconds.

You don’t mention the year of the vehicle. But some require that the alternator spin at a certain RPM for a certain amount of time to bring it on line.


There is a gauge not a light. Gauge doesn’t move until you use power such as headlights and it will read negative.

It is a 1983 Dodge D 150. The RPM’s are fine.

Fan Belt is new and all links and fuses are fine.

Take a look here:

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Thanks but I have and I have replace the Alternator and Voltage Regulator twice and have the same results.

You may have a broken wire or poor connection in the field control/voltage regulator circuits. Start by measuring the voltage on the field control connectors (blue and green wires) at the alternator with the engine running.

I checked them earlier today and they had a good reading it was over 12 volts

That is not good, the alternator won’t charge if both field wire have the same voltage. The voltage regulator triggers a ground on the green wire to cause the alternator to charge.

Measure the voltages on the wires at the voltage regulator.

Sometimes those barrel connectors on the voltage regulator become loose or corroded.

How can you test then at the voltage regulator with that big plug? If they are loose how do I fix this problem?

With the engine running at idle, right after a cold start (like first thing in the AM) what voltage do the battery posts measure? Connect your volt meter probes (in DC volt mode) between the + and - battery posts.

Next, under the same conditions, what voltage do you measure between the big wire coming out of the alternator and the - post on the battery? One probe right at the alternator, the other at the battery?

If everything working correctly both should read in the 13.5 - 15 volt range and both should be close to the same voltage.

When I need to probe an inaccessible connection and the usual back-probing method won’t work I’ll sometimes use a straight pin (like comes w/new dress shirts) to pierce the wire insulation to get the pin touching the conductor inside the insulation, and connect the volt meter probe to the pin. For obvious reasons, I only use this method on low voltage circuits. I’ve also resorted to cutting the wire and splicing in a test section with spade connectors on each end too.

Ok guys thanks for all of your suggestions but none if them have worked so far.

Just replace the wiring harness to the voltage regulator and see what happens. Should be a quick and easy thing to try.

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If there are two field wires going to the alternator and they are green and blue it appears ignition power should be applied to the alternator via the blue wire. The green wire should tie to ground through the big plug and the voltage regulator. Be sure the regulator has a good ground to it. Check the voltage between the green lead going to the alternator and the regulator connections. with the engine running. If the connection is good there should be very little voltage across the wire connections. Make sure the alternator has the proper ground connection made to it also.

Been there done that with no results

This is not a difficult charging system to diagnose but you will need a volt meter.

If you could post the results we can move on with the diagnoses. Also measure the voltage of the voltage regulator chassis to ensure it is grounded.

Your response to my previous post stated you had no results. By this I assume you mean that the green wire had no voltage across it and you show battery voltage on that wire connection going to the regulator and ground. If that is the case and the regulator controls the ground connection going to the alternator field circuit then the trouble would have to be related to the regulator operation. Like a lack of power to the regulator it or lack of a connection to ground.