Since you said the voltage is 10V and dropping, I suspect the alternator (specifically the regulator) since the battery light goes off when you accelerate. If the voltage is below 12.5v, it's most likely the charging system (alternator, regulator). If that is the case, if you can, check the voltage directly from the alternator while the engine is running. If it's around 13v, your alternator is fine, if not, it's bad. This has been one fault in all of the Ford's I've owned. Hopefully that is all it is, and nothing else. One more thing, check the positive cables running from the alternator to the starter, and the starter to the battery. Your problem may also lie somewhere in there. Good luck!
Sean
