Battery light on.

some ford vehicles have an external voltage regulator. when theres more demand for power it gives it. but when theres too much itll lower it so it does not overcharge. at 1600 rpms there is more demand, plugs firing with more fuel in the cyl, if the alt is working properly the regulator could mess up and stop power from the alt. its a cheap fix or tryout...another big problem is ground if the system does not have an adequate ground nothin would work as it should.

sounds like the rotor is flying open the part store cant get the unti up to high enuff rpm to see the problem