What could cause my 88 f150 pu charging system to stop charging?

Hi David,

Generally there are three main parts to your charging system, the alternator, voltage regulator and battery, and any one of those three parts can cause the charging to not work.

The battery has a certain capacity for holding an electrical charge, and over time it can lose the ability to maintain a charge.

The voltage regulator takes the AC-rectified waveform from the alternator and converts it to a steady DC voltage to both power the car and charge the battery. In older generation vehicles the regulator was a separate component from the alternator, but modern cars incorporate the regulator into the alternator.

The alternator is responsible for converting the motion of a spinning stator into electricity. It generates a sine wave, which then goes through a set of rectifiers to invert the negative-going part of the sine wave to positive voltage.

Testing is usually not too difficult; you'll want to figure out if it's the battery or the alternator first. With the car running you should see a voltage on the battery terminals of roughly 14 volts DC. When the car is turned off it'll be about 12V. If the voltage doesn't increase with the car running, you should take the alternator out and get it tested. If it does show about 14V, then you'll want to pull the battery and have it tested.

Most auto parts stores will test either or both for free. When you take the battery in for testing, it's best to have put it on a battery charger to make sure it's as charged as it can be to get an accurate test.

If the alternator isn't putting out the voltage it should, generally there are two parts to look at. First thing is the brushes; they just plain wear down and quit making contact. The good news is they're usually relatively cheap and simple to replace and that's often all that's needed to restore your alternator to service.

If the brushes are good, then the next most likely failure is the voltage regulator. Again, that's usually not too difficult to replace and will be substantially cheaper than replacing the entire alternator. If you have it tested at the auto parts store depending on their level of expertise they may be able to tell you if the regulator has failed. The brushes you can usually tell by looking at; if they're not or barely reaching the contacts then you need new ones.