The Ford troubleshooting guide says to do the following for poor antenna reception.
1. Check the resistance between antenna ground plate and battery ground cable. The resistance should be less than 5 ohms between the antenna ground plate and the battery ground cable. The antenna ground plate is located under the headliner. If the resistance is greater than 5 ohms go to step #2. If 5 ohms or less go to step #3.
2. Check the antenna cable connections including the extension cable. Are the connections clean, secure and in metal to metal contact?
3. Check the suppression equipment mounting and connecting circuits.
I doubt that the ground plate has loosened or become corroded. I would first check the battery ground first. Clean the battery terminal and attachment points. Corrosion from the battery ground occurs slowly over time which may be the culprit. Also check the ground strap between the hood and body.
If the antenna reception is still bad after checking the grounds and all antenna connections the Ford manual tells the technicians in step #3 to make sure there is good metal to metal contact in the supression equipment (a ground issue again). Then if needed test the suppression equipment by replacing each individual piece (there are three listed. (2) capacitive bond wires and (1) interference capacitor bolt) by replacing one at a time with a known good or new part and re-testing.
I have been looking for an external antenna for my 2001 Windstar because of the overall poor AM reception. Saw a new roof mount antenna system at SEMA in Las Vegas. It looks like what you see on a BMW. They claim AM reception better than an external pole antenna and FM reception equal to that of an in glass antenna.
http://www.skyyear.com/index.asp?Pag...ATS&Category=2