Questions and Answers
Exciting Ford Alternator
Q. Ok here is my problem. I have a 1997 Ford Contour V-6 2.5 liter manual with about 69,000 miles on it, with cruise control and A/C. When I get in the car each morning the battery light stays on for about a mile. It does this every time I start my car. I have taken it in to a place and had the battery checked and had a electrical system check done on the car.
It seems to run fine, but what is causing the battery light to be on when the vehicle is first started and what do I need to do to fix this? My dad was a mechanic for 29 years and can't figure it out either. Please help me, I'm afraid someday something is going to happen to the car and I will be stuck somewhere.
A. I suspect the problem is inside the alternator, specifically, the voltage regulator. An alternator needs a shoot of current to start working. This is called "Exciting".
The integral voltage regulator varies rotor field excitation according to the electric current demand of the vehicle. With the ignition switch in the RUN position voltage is applied through the charge indicator circuit to the alternator (GEN). The alternator is turned on, allowing current to flow from the battery sense circuit to the alternator field coil.
When the engine is started the alternator begins to generate Alternating (AC) current which is converted to Direct Current (DC) by the rectifier assembly, which is internal to the alternator. Current is then supplied to the vehicle's electrical system through the output stud located on the rear of the alternator.
What I suspect is happening is that the VR is not exciting the alternator and is not charging. Apparently when the VR gets warm enough, it then supplies the excite current and the alternator starts charging.
Naturally when it starts working and you have it checked, it checks out good. Ideally the system should be checked when the light is on. I think replacing the alternator will fix the problem.
Additional Information provided courtesy of ALLDATA
