I thought I would put a few thoughts here on something that may help you troubleshoot radio static problems.

I'm talking about a specific problem this time. Static only when you use the AC or rear window defroster (for your non-Ranger vehicles). Those don't seem to have anything in common, but they do. They both draw a lot of current (amps).

An alternator produces three phase AC current which is fed to a rectifier system of (usually) 6 diodes. This turns the AC into DC with just a small amount of ripple in it. The battery acts kind of like a filter so that this ripple doesn't affect anything.

If one or more of the diodes fail, that small ripple will become much bigger. When you turn on the high current item, the current feeding the radio will become a sawtooth wave generating a lot of noise.

Here is how to check your alternator with a good digital multimeter. Set the meter to the lowest AC Voltage range (Yes, AC). Put the black lead on the negative battery post and the red lead on the positive battery post. Run the engine at about 1500 RPM. Turn on the AC full blast and the rear defroster.

You should not read more 0.09 volts AC. If you do, you must rebuild or replace the alternator. I hope I just solved someone's problem.

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2005 2.3L XL 5SOD 3.73 K&N
KYB Shocks Husky Toolbox
Alpine / Rockford Fosgate Sound

"Ask me about my AC Vent fix!"