DO NOT REMOVE THE BATTERY CABLE WHILE THE ENGINE IS RUNNING! That is a real easy way to destroy every computer on the car. It's a trick that was done many years ago by mechanics who didn't understand how these simple circuits work.
If rasmatz's recommendation doesn't lead to the problem, have the generator tested or you can do a proper test yourself with an inexpensive digital voltmeter, but these tests must be done while the problem is acting up. Measure the battery voltage when the engine is running. It must be between 13.75 and 14.75 volts.
It's common for many brands of generators to fail completely but Fords also have more than their share of diode problems. One defective diode out of the six will reduce the generator's maximum output to one third of its rated capacity, but more importantly, since one of the three phases is lost, the "ripple" will be extremely high. That means there will be a dropout in the voltage one third of the time. The voltage regulator will try to adjust for that by raising output. Without the battery in the circuit to help control voltage and smooth that ripple, it is real easy for system voltage to go to over 30 volts. I did that once every year as a demonstration for my students to show why we NEVER remove the battery cable. Every time I did that, I sacrificed a generator, but I made sure it was on an older car with no computers. That high voltage will also destroy the diodes in the generator and can take out the voltage regulator.
The battery voltage could still be between 13.75 and 14.75 volts if the generator has a bad diode. To test accurately for that you will need a load tester. The equipment most mechanics use will also measure ripple. If it is excessive and if the maximum output is down to around 25 to 35 amps, there is a defective diode and it will be easier to just replace the entire generator.
Also be aware that around this time period Ford used a bunch of generators with two fat output wires in a plug-in connector on the side. They are black with an orange stripe. This was a brilliant idea, of which they have many. You are to never remove that connector because it will degrade the integrity of the connections and cause the terminals to burn up. It's bad enough to expect each terminal to pass 50 amps but when one develops a little resistance and overheats, it makes the other one carry the full load; then it's just a matter of time before it too burns up. Rebuilt generators come with that plug already installed. You are expected to cut and splice the wires. You would think the brains at Ford could have thought of something better but they do seem to be fond of engine fires in their vehicles. Building electrical systems like that just begs for problems caused by do-it-yourselfers, but even professionals are not aware of many of these things and can run into trouble. If you have the single fat output wire BOLTED to the back of your generator, you don't have to worry about this issue.
Wednesday, April 27th, 2011 AT 10:11 PM