This issue has just started in the past couple of weeks. I have a 2003 E350 SuperDuty 5.4l gas, radio is cheapo aftermarket. It has about 155,000 miles on it, most of those as a handicap van. All of the wheelchair lift electronics have been removed and the van has been working great since I got it in November 2017.

Once I turn the ignition off the radio will stay on; everything else (dash lights, etc) all turn off. It seems like something is being energized (or perhaps a relay is stuck on) while the ignition is on. However, if I turn the windshield wipers on while the ignition is off, the radio will then fade out. There is not enough electrical charge to move the wipers but the resistance of the wiper motor is enough to discharge the 'ghost' current. The engine starting battery is fairly old but the resting voltage is 12.66. I have converted this van into a camper van with a separate electrical system for the back of the van; the only connection between the 2 systems in a manual switch which I leave in the off position. The only other thing that might be affecting this is the ignition switch itself--the key lock is wore out and I can start the van without the key in. I can still lock the steering wheel if I rotate the key all the way counter-clockwise and then I need the key to unlock the switch and the steering wheel.

Any ideas on this or how to track down the root of the problem?

 

I wonder if the worn out key switch is allowing the ignition/start switch to go into the accessory position? I owned/drove a 2003 E350 for 12 years but don't remember if it had an accessory position counter clockwise one click back from off. I'd start with a new key switch.

 

On my '98 E150 I had issues with that damn Multifunction Switch that I had to resort to a floor mounted dimmer switch. I think that it's on account of the miniscule wiring the manufaturers are using these days. I suspect in my case the wiring was simply overtaxed.