Hi cougarman. Don't know what the problem is. Sometimes people just have a bad day. Do the lights flicker real fast, like a couple of times per second? Or do they get brighter for a while, then suddenly dim down for a few seconds? I'm assuming the battery light doesn't turn on. Set me straight if I'm wrong.
If the battery light doesn't turn on, the generator is continuing to produce output and the voltage regulator is not turning on the light. Two things inside the generator that can cause a fluctuation in voltage are the regulator itself and a shorted diode, and neither of those is very likely to be intermittent. If they are, you would find that by monitoring the voltage right at the output terminal with a digital voltmeter.
What is much more common is when Ford uses the battery stud on the starter relay as a convenient tie point. Very often the high current loosens the copper nut and creates an intermittent connection. A good place to start is by removing those terminals and cleaning them up. In the past, that was used as the starter solenoid and passed the really high starter current so it would also cause intermittent cranking. On newer cars it is just the relay even though it's the same physical part, so it doesn't pass the starter current, but it is where the other circuitry originates from.
You might also measure the voltage right across the battery terminals while the engine is running and the problem is occurring. If you see it varying there, try a new battery. GM has a huge problem with their generators because they produce big voltage spikes that can destroy the diodes and voltage regulator. Those spikes are absorbed and dampened by the battery. As it ages, the battery loses its ability to dampen those spikes and repeat failures of the generator occur. It would seem logical that the same thing happens to batteries in other cars too.
Look for ground wires corroded off between the engine and body. If you still haven't found the problem, try running a temporary wire right from the generator's output terminal to the battery positive post. If the lights still flicker, I guess I would suspect the generator itself, but I would want to eliminate everything else first.
At some point Ford stopped using the starter relay on the inner fender. If you have a little plug-in relay in the fuse box, disregard my description of the relay connections. Look for a smaller positive battery cable that bolts to the under-hood fuse box. Every brand and model of car at some point has had that cable work loose and cause intermittent problems.
One more thing you might consider is measuring the voltage to other circuits to see if just the lights are involved or if the entire system voltage is affected. Motor circuits are bad things to monitor with a digital voltmeter because the voltage fluctuations will be picked up by the meter, so look for something else to check like the circuit that feeds the power locks. Actually, you CAN use the motor circuits, but it's more accurate if the motor isn't running. The feed for the power windows is one example. You're just trying to see what is affected besides the lights.
If you find the voltage varying all over, try using different points to ground the voltmeter. If the voltage holds steady with different ground points, that would suggest a ground cable or connection problem. We tend to get wrapped up in the positive feed circuit when the ground circuit is just as likely to develop a problem.
If none of these things pans out, I'll try to find the wiring diagram on Ford's web site so we can come up with some more ideas.
Wednesday, April 13th, 2011 AT 6:23 PM