Over the past couple of months my battery light.

ANONYMOUS

MEMBER
2002 FORD ESCAPE
200,000 MILES

Over the past couple of months my battery light has been coming on and off. Last night while driving my heater blower motor sounded like it went into turbo and when I would hit the brakes all my idiot lights would come on and my tach and speedometer stopped working. Today when I went to start it my battery was completely dead. I jump started it and disconnected the battery to see if my alternator was shot. When I disconnected not only did my engine keep running but my windshield wipers came on high by themselves and my idiot lights all came on again. When I connected the battery only the ABS lights stayed on.

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

DO NOT DISCONNECT THE BATTERY CABLE WITH THE ENGINE RUNNING!!!!!!!!!!!

That is a real easy way to destroy every computer on the vehicle. I did that every year on the test bench to demonstrate for my students what can happen. System voltage can easily go to over 30 volts and destroy everything that is turned on. Doing that procedure was done many years ago on cars without computers, by mechanics who didn't understand how to diagnose these simple circuits. Those days are gone. Do that once at the dealership I worked at and you'd get a long, stern lecture in the manager's office. Do that twice and you were out-the-door.

The battery is also the key component in helping to dampen and absorb "ripple" and the voltage spikes generators can produce. Those spikes can destroy the built-in voltage regulator and diodes, and they can interfere with computer sensor signals, so you can ignore for now any warning lights that turned on. They are the result of confused computers and should not be used as troubleshooting clues. Those spikes are a REAL big problem for GM owners of '87 and newer vehicles, . . . Ford and Chrysler owners, not so much, as long as the battery stays connected.

The fact that the engine stayed running doesn't prove anything because you have an intermittent problem and any testing has to be done while the problem is occurring. The easiest way to tell if the charging system is working is to measure the battery voltage with the engine running. It must be between 13.75 and 14.75 volts. If it is low, you have to determine if it's a generator or voltage regulator problem, and Ford makes that real easy for you. At least it was in the '90s. Take a look at this page to see how to bypass the regulator to see if the rest of the system is working:

http://randysrepairshop.net/ford-ac-generator-with-built-in-regulator.html

Intermittent problems can be caused by loose or corroded wiring and terminals, or in your case a corroded fuse, but 99 percent of the time it is due to worn brushes in the generator. That web page shows how to test for that. The brushes come as part of a new voltage regulator. You might even find them available separately at some parts stores. On many vehicles the regulator can be removed without even removing the generator from the engine.