…But is just fine in Park or neutral. I suspect the Neutral Safety Switch, but before I buy parts and tear into it I’d like to be sure.
Does the radio mute the audio, but have the display stay on?
Or, does the radio stop and the display blank when this happens? I suspect that this is the case. What’s happening is that the radio is designed to shutdown while the engine is being started, even though it is powered at that time. The start signal that is applied to the stater solenoid is also connected to the radio. The radio shuts down when that signal goes high.
You may have an issue with the neutral safety switch, but that is unlikely. More likely is that the pulldown resistor in the radio isn’t working.
Look at the diagram in this link.
Add a 1000 ohm, 1/4 or 1/2 watt resistor between the start wire (pin 16) and ground (pin 13), and you should be good to go.
At first I was on the same page as you, but actually the radio does stay on, and does not act like you put the ignition in the start position. It’s very repeatable, as soon as you shift to drive the radio mutes. It doesn’t say mute of the screen, but all audio cuts out. You can go to any drive and reverse gear and it’ll do it. Neutral and park and the audio comes right back.
Weird. Maybe you should try one of the Ford truck forums.
(As a test, you could try pulling the start wire out of the radio connector and see if the problem stays or goes away. The wire and pin can be pulled out without damage and then reinserted after the test.)
I checked out some ford forums, I got a few leads from the Ranger forums, but it wasn’t until I included all Ford makes and models did this start coming up as a common issue.
As you can now imagine, this is how my work day has been consumed. 