Expert: Ben Deutschman - 1/21/2011

Question
Ben I'm hoping you can give me some insight.  I am having an intermittent problem with my 2007 Ford E-250 work truck.  Sometimes when I turn on the headlights, while the vehicle is in any gear, forward - reverse the vehicles radio will shut off.  If I turn off the headlights the radio comes back on while still in gear.  If I shift the vehicle to park or neutral with the lights on the radio will continue to function normally.  I've checked all the fuses as has my company's fleet mechanic and nothing obvious was noticed.  My fleet mechanic is stumped.  My question is do you think there could be some relay that is intermittently hung up when the vehicle is put in gear and discontinues power to the radio?  All other functions of the vehicle i.e. turn signals, dome lights, hazard lights, fan etc. work normally and are not affected by the headlights coming on.

Thanks for your time and effort in advance.

Answer
It sounds like your Alternator isn't charging enough when the vehicle is idling in gear. If you have a Volt/Amp tester, you can find out if the Alternator is putting out what is supposed to be. You would also need a Haynes, Chilton's, or factory Shop Manual in order to know what the correct Voltage and Amperage outputs are for your vehicle's Alternator.If you don't have a Test Meter, then you can go to an Autozone store, Advance Auto Parts, or O'Reilly's Auto Parts, and usually they will test your Alternator for free.