Trying to sort out car radio reception problems can be an absolute nightmare! Here are a few hints to get you started.
First, put the ignition key to the first position (which simply allows you to turn the radio and other electrical accessories on) and try tuning through a few stations, both on AM and FM (assuming, of course that your radio actually has AM. - some cheaper Ford cars don't). If reception is already poor, the problem is either because of a fault with the aerial (such as a poor connection somewhere) or because the radio is badly earthed.
However, if reception is fine with the ignition key in that position, try turning it to 'position 2' (without actually starting the engine). If radio reception is now suddenly degraded, there's a fault with something in the car's electrics which is causing interference and blocking incoming signals. Remove, and then replace, each fuse in turn to track down where the problem lies. (I had a Citroen BX where the radio reception all but disappeared when the ignition key was in 'position 2'. Removing the fuses helped me find out that there was an otherwise undetectable electrical fault within the rear wiper motor which, I'll think you'll agree, isn't the first place most people would think to look when trying to fix their car radio!).
If reception is still fine with the key in 'position 2', start the engine. If reception is now suddenly degraded, the problem is linked in some way to interference from the engine. (An 'rf choke', from a motor spares shop, placed into the power lead to the radio might fix the problem).
However, you can save yourself all of that bother by simply upgrading to DAB and installing one of these:
http://www.pure.com/products/product.asp?Produ ct=VL-60905
(Around �65 in shops. Slightly cheaper online).
Chr