[Towncar]

Well, that was an interesting question

I did some poking around for you and came up with several links that will help you with your EXTREMELY general question.

Take a look at some of these references:
http://www.tune-town.com/Cars/stuff/...n_Town_Car.htm
http://www.tune-town.com/technical.asp
http://www.radiosandmore.com/AdvancedSearch.asp
http://www24.brinkster.com/sdhartney...jblstereo.htm#

Look for reply from Charles:
http://www.lincolnsonline.com/cgi-bi...&f=19&t=000107

Check RJ's post:
http://www.lincolnsonline.com/cgi-bi...&f=19&t=000018

tvmodular always takes these issues to the extreme:
http://www.p71interceptor.com/radio/
http://www.p71interceptor.com/radio/selftest.html